phase 6+7+8: model loading, BPE tokenizer, GPT-2 inference (Milestone ①)

Phase 6 — Model Loading (xserv-model): - safetensors parser with single/sharded file support - ModelConfig with dual naming (GPT-2 n_embd/n_head + modern HF naming) - Weight loading flow: safetensors → mmap → CPU Tensor → GPU Phase 7 — BPE Tokenizer (xserv-tokenizer): - Full BPE encode/decode from tokenizer.json - GPT-2 byte-to-unicode mapping (printable ASCII identity + shifted bytes) - Pre-tokenization regex, special token handling - Chat template support structure Phase 8 — GPT-2 Complete Inference: - GPT-2 model definition: wte, wpe, 12 transformer blocks, ln_f - Forward pass: embedding → (LayerNorm → MHA → residual → LayerNorm → MLP → residual) × 12 → LN → logits - QKV split with correct [batch, heads, seq, dim] layout (fixed reshape bug) - Greedy sampling from last-position logits - Interactive CLI: xserv-cli <model-dir> [--max-tokens N] Verified: GPT-2 124M generates coherent English text on RTX 5090. "The future of AI is uncertain. The future of AI is uncertain..." "Once upon a time, the world was a place of great beauty..." Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
phase 5: naive multi-head attention
2026-05-21 22:04:00 +08:00 · 2026-05-21 21:17:23 +08:00 · 2026-05-21 21:07:24 +08:00 · 2026-05-21 20:59:45 +08:00
39 changed files with 3148 additions and 19 deletions
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -4,6 +4,8 @@ members = [
    "crates/xserv-cuda",
    "crates/xserv-tensor",
    "crates/xserv-kernels",
+    "crates/xserv-model",
+    "crates/xserv-tokenizer",
 ]

 [workspace.package]
@@ -14,3 +16,7 @@ license = "MIT"
 [workspace.dependencies]
 half = "2"
 smallvec = "1"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+safetensors = "0.5"
+regex = "1"
--- a/crates/xserv-kernels/build.rs
+++ b/crates/xserv-kernels/build.rs
@@ -13,9 +13,17 @@ fn main() {
        .cuda(true)
        .cudart("shared")
        .flag("-gencode=arch=compute_120,code=sm_120")
+        .include("../../csrc")
        .file("../../csrc/gemm/naive.cu")
        .file("../../csrc/gemm/tiled.cu")
-        .compile("xserv_gemm_kernels");
+        .file("../../csrc/normalization/rmsnorm.cu")
+        .file("../../csrc/normalization/layernorm.cu")
+        .file("../../csrc/activation/activations.cu")
+        .file("../../csrc/reduce/softmax.cu")
+        .file("../../csrc/embedding/embedding.cu")
+        .file("../../csrc/embedding/rope.cu")
+        .file("../../csrc/attention/causal_mask.cu")
+        .compile("xserv_kernels");

-    println!("cargo:rerun-if-changed=../../csrc/gemm/");
+    println!("cargo:rerun-if-changed=../../csrc/");
 }
--- a/crates/xserv-kernels/src/activation.rs
+++ b/crates/xserv-kernels/src/activation.rs
@@ -0,0 +1,59 @@
+use std::ffi::c_void;
+use xserv_tensor::{DType, Device, Tensor};
+
+unsafe extern "C" {
+    fn launch_gelu_f32(x: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
+    fn launch_gelu_bf16(x: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
+    fn launch_silu_f32(x: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
+    fn launch_silu_bf16(x: *const c_void, out: *mut c_void, n: i32, stream: *mut c_void);
+    fn launch_scale_f32(x: *const c_void, out: *mut c_void, scale: f32, n: i32, stream: *mut c_void);
+    fn launch_scale_bf16(x: *const c_void, out: *mut c_void, scale: f32, n: i32, stream: *mut c_void);
+}
+
+pub fn gelu(x: &Tensor) -> Tensor {
+    assert!(x.is_contiguous());
+    assert!(matches!(x.device(), Device::Cuda(_)));
+    let out = Tensor::zeros(x.shape(), x.dtype(), x.device());
+    let n = x.numel() as i32;
+    unsafe {
+        match x.dtype() {
+            DType::F32 => launch_gelu_f32(x.data_ptr() as _, out.data_ptr() as *mut c_void, n, std::ptr::null_mut()),
+            DType::BF16 => launch_gelu_bf16(x.data_ptr() as _, out.data_ptr() as *mut c_void, n, std::ptr::null_mut()),
+            _ => panic!("unsupported dtype for gelu"),
+        }
+    }
+    xserv_cuda::device::synchronize().unwrap();
+    out
+}
+
+pub fn silu(x: &Tensor) -> Tensor {
+    assert!(x.is_contiguous());
+    assert!(matches!(x.device(), Device::Cuda(_)));
+    let out = Tensor::zeros(x.shape(), x.dtype(), x.device());
+    let n = x.numel() as i32;
+    unsafe {
+        match x.dtype() {
+            DType::F32 => launch_silu_f32(x.data_ptr() as _, out.data_ptr() as *mut c_void, n, std::ptr::null_mut()),
+            DType::BF16 => launch_silu_bf16(x.data_ptr() as _, out.data_ptr() as *mut c_void, n, std::ptr::null_mut()),
+            _ => panic!("unsupported dtype for silu"),
+        }
+    }
+    xserv_cuda::device::synchronize().unwrap();
+    out
+}
+
+pub fn scale(x: &Tensor, scale_val: f32) -> Tensor {
+    assert!(x.is_contiguous());
+    assert!(matches!(x.device(), Device::Cuda(_)));
+    let out = Tensor::zeros(x.shape(), x.dtype(), x.device());
+    let n = x.numel() as i32;
+    unsafe {
+        match x.dtype() {
+            DType::F32 => launch_scale_f32(x.data_ptr() as _, out.data_ptr() as *mut c_void, scale_val, n, std::ptr::null_mut()),
+            DType::BF16 => launch_scale_bf16(x.data_ptr() as _, out.data_ptr() as *mut c_void, scale_val, n, std::ptr::null_mut()),
+            _ => panic!("unsupported dtype for scale"),
+        }
+    }
+    xserv_cuda::device::synchronize().unwrap();
+    out
+}
--- a/crates/xserv-kernels/src/attention.rs
+++ b/crates/xserv-kernels/src/attention.rs
@@ -0,0 +1,77 @@
+use std::ffi::c_void;
+use xserv_tensor::{DType, Tensor};
+
+use crate::activation::scale;
+use crate::gemm::batched_matmul;
+use crate::softmax::softmax;
+
+unsafe extern "C" {
+    fn launch_causal_mask_f32(scores: *mut c_void, batch: i32, rows: i32, cols: i32,
+                              offset: i32, stream: *mut c_void);
+    fn launch_causal_mask_bf16(scores: *mut c_void, batch: i32, rows: i32, cols: i32,
+                               offset: i32, stream: *mut c_void);
+}
+
+fn apply_causal_mask(scores: &Tensor, offset: usize) {
+    let ndim = scores.ndim();
+    let rows = scores.shape()[ndim - 2];
+    let cols = scores.shape()[ndim - 1];
+    let batch: usize = scores.shape()[..ndim - 2].iter().product();
+
+    unsafe {
+        match scores.dtype() {
+            DType::F32 => launch_causal_mask_f32(
+                scores.data_ptr() as *mut c_void,
+                batch as i32, rows as i32, cols as i32, offset as i32,
+                std::ptr::null_mut(),
+            ),
+            DType::BF16 => launch_causal_mask_bf16(
+                scores.data_ptr() as *mut c_void,
+                batch as i32, rows as i32, cols as i32, offset as i32,
+                std::ptr::null_mut(),
+            ),
+            _ => panic!("unsupported dtype for causal mask"),
+        }
+    }
+    xserv_cuda::device::synchronize().unwrap();
+}
+
+/// Multi-head attention (naive, materializes S×S score matrix).
+///
+/// q, k, v: [batch, num_heads, seq_len, head_dim] — contiguous, on GPU
+/// Returns: [batch, num_heads, seq_len, head_dim]
+pub fn attention(q: &Tensor, k: &Tensor, v: &Tensor, causal: bool) -> Tensor {
+    assert_eq!(q.ndim(), 4);
+    assert_eq!(k.ndim(), 4);
+    assert_eq!(v.ndim(), 4);
+    assert!(q.is_contiguous() && k.is_contiguous() && v.is_contiguous());
+
+    let batch = q.shape()[0];
+    let num_heads = q.shape()[1];
+    let q_len = q.shape()[2];
+    let head_dim = q.shape()[3];
+    let kv_len = k.shape()[2];
+
+    assert_eq!(k.shape(), &[batch, num_heads, kv_len, head_dim]);
+    assert_eq!(v.shape(), &[batch, num_heads, kv_len, head_dim]);
+
+    // scores = Q @ K^T → [B, H, q_len, kv_len]
+    let k_t = k.transpose(2, 3).contiguous();
+    let scores = batched_matmul(q, &k_t);
+
+    // Scale by 1/sqrt(head_dim)
+    let scale_factor = 1.0 / (head_dim as f32).sqrt();
+    let scaled_scores = scale(&scores, scale_factor);
+
+    // Causal mask
+    if causal {
+        let offset = kv_len - q_len;
+        apply_causal_mask(&scaled_scores, offset);
+    }
+
+    // Softmax
+    let weights = softmax(&scaled_scores);
+
+    // output = weights @ V → [B, H, q_len, head_dim]
+    batched_matmul(&weights, v)
+}
--- a/crates/xserv-kernels/src/embedding.rs
+++ b/crates/xserv-kernels/src/embedding.rs
@@ -0,0 +1,51 @@
+use std::ffi::c_void;
+use xserv_cuda::GpuBuffer;
+use xserv_tensor::{DType, Device, Tensor};
+
+unsafe extern "C" {
+    fn launch_embedding_f32(table: *const c_void, token_ids: *const c_void, out: *mut c_void,
+                            num_tokens: i32, hidden_size: i32, stream: *mut c_void);
+    fn launch_embedding_bf16(table: *const c_void, token_ids: *const c_void, out: *mut c_void,
+                             num_tokens: i32, hidden_size: i32, stream: *mut c_void);
+}
+
+/// Embedding lookup: table[token_ids[i]] for each i.
+/// table: [vocab_size, hidden_size], token_ids: [num_tokens] (i32 on CPU)
+pub fn embedding(table: &Tensor, token_ids: &[u32]) -> Tensor {
+    assert_eq!(table.ndim(), 2);
+    assert!(table.is_contiguous());
+    assert!(matches!(table.device(), Device::Cuda(_)));
+
+    let hidden_size = table.shape()[1];
+    let num_tokens = token_ids.len();
+
+    // Upload token_ids to GPU
+    let ids_bytes = unsafe {
+        std::slice::from_raw_parts(
+            token_ids.as_ptr() as *const u8,
+            num_tokens * std::mem::size_of::<u32>(),
+        )
+    };
+    let mut ids_gpu = GpuBuffer::alloc(ids_bytes.len()).expect("alloc token_ids");
+    ids_gpu.copy_from_host(ids_bytes).unwrap();
+
+    let out = Tensor::zeros(&[num_tokens, hidden_size], table.dtype(), table.device());
+
+    unsafe {
+        match table.dtype() {
+            DType::F32 => launch_embedding_f32(
+                table.data_ptr() as _, ids_gpu.as_ptr() as _,
+                out.data_ptr() as *mut c_void,
+                num_tokens as i32, hidden_size as i32, std::ptr::null_mut(),
+            ),
+            DType::BF16 => launch_embedding_bf16(
+                table.data_ptr() as _, ids_gpu.as_ptr() as _,
+                out.data_ptr() as *mut c_void,
+                num_tokens as i32, hidden_size as i32, std::ptr::null_mut(),
+            ),
+            _ => panic!("unsupported dtype for embedding"),
+        }
+    }
+    xserv_cuda::device::synchronize().unwrap();
+    out
+}
--- a/crates/xserv-kernels/src/gemm.rs
+++ b/crates/xserv-kernels/src/gemm.rs
@@ -46,6 +46,19 @@ unsafe extern "C" {
        compute_type: i32,
        algo: i32,
    ) -> i32;
+    fn cublasGemmStridedBatchedEx(
+        handle: CublasHandle,
+        transa: i32, transb: i32,
+        m: i32, n: i32, k: i32,
+        alpha: *const c_void,
+        a: *const c_void, a_type: i32, lda: i32, stride_a: i64,
+        b: *const c_void, b_type: i32, ldb: i32, stride_b: i64,
+        beta: *const c_void,
+        c: *mut c_void, c_type: i32, ldc: i32, stride_c: i64,
+        batch_count: i32,
+        compute_type: i32,
+        algo: i32,
+    ) -> i32;
 }

 pub struct CublasContext {
@@ -149,3 +162,68 @@ pub fn matmul(a: &Tensor, b: &Tensor, backend: GemmBackend) -> Tensor {

    c
 }
+
+/// Batched matrix multiplication via cuBLAS: C[b] = A[b] @ B[b]
+/// a: [..., M, K], b: [..., K, N] → [..., M, N]
+/// Leading dimensions must match and tensors must be contiguous.
+pub fn batched_matmul(a: &Tensor, b: &Tensor) -> Tensor {
+    assert!(a.ndim() >= 2 && b.ndim() >= 2);
+    assert_eq!(a.ndim(), b.ndim());
+    assert!(a.is_contiguous() && b.is_contiguous());
+    assert!(matches!(a.device(), Device::Cuda(_)));
+    assert_eq!(a.dtype(), b.dtype());
+
+    let ndim = a.ndim();
+    let m = a.shape()[ndim - 2];
+    let k = a.shape()[ndim - 1];
+    let n = b.shape()[ndim - 1];
+    assert_eq!(b.shape()[ndim - 2], k, "inner dimension mismatch");
+
+    // Compute batch count from leading dimensions
+    let batch: usize = a.shape()[..ndim - 2].iter().product();
+    assert_eq!(
+        b.shape()[..ndim - 2].iter().product::<usize>(),
+        batch,
+        "batch dimensions mismatch"
+    );
+
+    let mut out_shape: Vec<usize> = a.shape()[..ndim - 2].to_vec();
+    out_shape.push(m);
+    out_shape.push(n);
+    let c = Tensor::zeros(&out_shape, a.dtype(), a.device());
+
+    let dtype = a.dtype();
+    let (a_type, b_type, c_type) = match dtype {
+        DType::F32 => (CUDA_R_32F, CUDA_R_32F, CUDA_R_32F),
+        DType::BF16 => (CUDA_R_16BF, CUDA_R_16BF, CUDA_R_16BF),
+        _ => panic!("unsupported dtype for batched matmul"),
+    };
+
+    let alpha = 1.0f32;
+    let beta = 0.0f32;
+    // cuBLAS strides are in elements (not bytes)
+    let stride_a = (m * k) as i64;
+    let stride_b = (k * n) as i64;
+    let stride_c = (m * n) as i64;
+
+    let ctx = CublasContext::new().unwrap();
+    unsafe {
+        cublasSetStream_v2(ctx.handle, std::ptr::null_mut());
+        // Row-major trick: C = A @ B ⟺ C^T = B^T @ A^T (col-major)
+        error::check(cublasGemmStridedBatchedEx(
+            ctx.handle,
+            CUBLAS_OP_N, CUBLAS_OP_N,
+            n as i32, m as i32, k as i32,
+            &alpha as *const f32 as *const c_void,
+            b.data_ptr() as _, b_type, n as i32, stride_b,
+            a.data_ptr() as _, a_type, k as i32, stride_a,
+            &beta as *const f32 as *const c_void,
+            c.data_ptr() as *mut c_void, c_type, n as i32, stride_c,
+            batch as i32,
+            CUBLAS_COMPUTE_32F,
+            -1,
+        )).expect("cuBLAS batched GEMM failed");
+    }
+    xserv_cuda::device::synchronize().unwrap();
+    c
+}
--- a/crates/xserv-kernels/src/layernorm.rs
+++ b/crates/xserv-kernels/src/layernorm.rs
@@ -0,0 +1,39 @@
+use std::ffi::c_void;
+use xserv_tensor::{DType, Device, Tensor};
+
+unsafe extern "C" {
+    fn launch_layernorm_f32(x: *const c_void, gamma: *const c_void, beta: *const c_void,
+                            out: *mut c_void, rows: i32, hidden_size: i32, eps: f32, stream: *mut c_void);
+    fn launch_layernorm_bf16(x: *const c_void, gamma: *const c_void, beta: *const c_void,
+                             out: *mut c_void, rows: i32, hidden_size: i32, eps: f32, stream: *mut c_void);
+}
+
+pub fn layernorm(x: &Tensor, gamma: &Tensor, beta: &Tensor, eps: f32) -> Tensor {
+    assert!(x.ndim() >= 1);
+    assert!(x.is_contiguous() && gamma.is_contiguous() && beta.is_contiguous());
+    assert!(matches!(x.device(), Device::Cuda(_)));
+    let hidden_size = *x.shape().last().unwrap();
+    assert_eq!(gamma.shape(), &[hidden_size]);
+    assert_eq!(beta.shape(), &[hidden_size]);
+
+    let rows = x.numel() / hidden_size;
+    let out = Tensor::zeros(x.shape(), x.dtype(), x.device());
+
+    unsafe {
+        match x.dtype() {
+            DType::F32 => launch_layernorm_f32(
+                x.data_ptr() as _, gamma.data_ptr() as _, beta.data_ptr() as _,
+                out.data_ptr() as *mut c_void,
+                rows as i32, hidden_size as i32, eps, std::ptr::null_mut(),
+            ),
+            DType::BF16 => launch_layernorm_bf16(
+                x.data_ptr() as _, gamma.data_ptr() as _, beta.data_ptr() as _,
+                out.data_ptr() as *mut c_void,
+                rows as i32, hidden_size as i32, eps, std::ptr::null_mut(),
+            ),
+            _ => panic!("unsupported dtype for layernorm"),
+        }
+    }
+    xserv_cuda::device::synchronize().unwrap();
+    out
+}
--- a/crates/xserv-kernels/src/lib.rs
+++ b/crates/xserv-kernels/src/lib.rs
@@ -1,3 +1,17 @@
+pub mod activation;
+pub mod attention;
+pub mod embedding;
 pub mod gemm;
+pub mod layernorm;
+pub mod rmsnorm;
+pub mod rope;
+pub mod softmax;

-pub use gemm::{GemmBackend, matmul};
+pub use activation::{gelu, scale, silu};
+pub use attention::attention;
+pub use embedding::embedding;
+pub use gemm::{batched_matmul, matmul, GemmBackend};
+pub use layernorm::layernorm;
+pub use rmsnorm::rmsnorm;
+pub use rope::{rope_inplace, RopeCache};
+pub use softmax::softmax;
--- a/crates/xserv-kernels/src/rmsnorm.rs
+++ b/crates/xserv-kernels/src/rmsnorm.rs
@@ -0,0 +1,37 @@
+use std::ffi::c_void;
+use xserv_tensor::{DType, Device, Tensor};
+
+unsafe extern "C" {
+    fn launch_rmsnorm_f32(x: *const c_void, gamma: *const c_void, out: *mut c_void,
+                          rows: i32, hidden_size: i32, eps: f32, stream: *mut c_void);
+    fn launch_rmsnorm_bf16(x: *const c_void, gamma: *const c_void, out: *mut c_void,
+                           rows: i32, hidden_size: i32, eps: f32, stream: *mut c_void);
+}
+
+pub fn rmsnorm(x: &Tensor, gamma: &Tensor, eps: f32) -> Tensor {
+    assert!(x.ndim() >= 1);
+    assert!(x.is_contiguous() && gamma.is_contiguous());
+    assert!(matches!(x.device(), Device::Cuda(_)));
+    let hidden_size = *x.shape().last().unwrap();
+    assert_eq!(gamma.shape(), &[hidden_size]);
+    assert_eq!(x.dtype(), gamma.dtype());
+
+    let rows = x.numel() / hidden_size;
+    let out = Tensor::zeros(x.shape(), x.dtype(), x.device());
+
+    unsafe {
+        match x.dtype() {
+            DType::F32 => launch_rmsnorm_f32(
+                x.data_ptr() as _, gamma.data_ptr() as _, out.data_ptr() as *mut c_void,
+                rows as i32, hidden_size as i32, eps, std::ptr::null_mut(),
+            ),
+            DType::BF16 => launch_rmsnorm_bf16(
+                x.data_ptr() as _, gamma.data_ptr() as _, out.data_ptr() as *mut c_void,
+                rows as i32, hidden_size as i32, eps, std::ptr::null_mut(),
+            ),
+            _ => panic!("unsupported dtype for rmsnorm"),
+        }
+    }
+    xserv_cuda::device::synchronize().unwrap();
+    out
+}
--- a/crates/xserv-kernels/src/rope.rs
+++ b/crates/xserv-kernels/src/rope.rs
@@ -0,0 +1,85 @@
+use std::ffi::c_void;
+use xserv_cuda::GpuBuffer;
+use xserv_tensor::{DType, Device, Tensor};
+
+unsafe extern "C" {
+    fn launch_rope_f32(x: *mut c_void, cos_cache: *const c_void, sin_cache: *const c_void,
+                       positions: *const c_void, num_tokens: i32, num_heads: i32,
+                       head_dim: i32, stream: *mut c_void);
+    fn launch_rope_bf16(x: *mut c_void, cos_cache: *const c_void, sin_cache: *const c_void,
+                        positions: *const c_void, num_tokens: i32, num_heads: i32,
+                        head_dim: i32, stream: *mut c_void);
+    fn launch_compute_rope_cache(cos_cache: *mut c_void, sin_cache: *mut c_void,
+                                 max_seq_len: i32, half_dim: i32, theta: f32,
+                                 stream: *mut c_void);
+}
+
+pub struct RopeCache {
+    pub cos: GpuBuffer,
+    pub sin: GpuBuffer,
+    pub max_seq_len: usize,
+    pub half_dim: usize,
+}
+
+impl RopeCache {
+    pub fn new(max_seq_len: usize, head_dim: usize, theta: f32) -> Self {
+        let half_dim = head_dim / 2;
+        let nbytes = max_seq_len * half_dim * std::mem::size_of::<f32>();
+        let mut cos = GpuBuffer::alloc(nbytes).expect("alloc cos_cache");
+        let mut sin = GpuBuffer::alloc(nbytes).expect("alloc sin_cache");
+
+        unsafe {
+            launch_compute_rope_cache(
+                cos.as_mut_ptr() as _, sin.as_mut_ptr() as _,
+                max_seq_len as i32, half_dim as i32, theta, std::ptr::null_mut(),
+            );
+        }
+        xserv_cuda::device::synchronize().unwrap();
+
+        Self { cos, sin, max_seq_len, half_dim }
+    }
+}
+
+/// Apply RoPE in-place to x.
+/// x: [num_tokens, num_heads, head_dim] on GPU
+/// positions: [num_tokens] (u32 on CPU, will be uploaded)
+pub fn rope_inplace(x: &Tensor, cache: &RopeCache, positions: &[u32]) {
+    assert_eq!(x.ndim(), 3);
+    assert!(x.is_contiguous());
+    assert!(matches!(x.device(), Device::Cuda(_)));
+    let num_tokens = x.shape()[0];
+    let num_heads = x.shape()[1];
+    let head_dim = x.shape()[2];
+    assert_eq!(head_dim / 2, cache.half_dim);
+    assert_eq!(positions.len(), num_tokens);
+
+    let pos_bytes = unsafe {
+        std::slice::from_raw_parts(
+            positions.as_ptr() as *const u8,
+            num_tokens * std::mem::size_of::<u32>(),
+        )
+    };
+    let mut pos_gpu = GpuBuffer::alloc(pos_bytes.len()).expect("alloc positions");
+    pos_gpu.copy_from_host(pos_bytes).unwrap();
+
+    unsafe {
+        match x.dtype() {
+            DType::F32 => launch_rope_f32(
+                x.data_ptr() as *mut c_void,
+                cache.cos.as_ptr() as _, cache.sin.as_ptr() as _,
+                pos_gpu.as_ptr() as _,
+                num_tokens as i32, num_heads as i32, head_dim as i32,
+                std::ptr::null_mut(),
+            ),
+            DType::BF16 => launch_rope_bf16(
+                x.data_ptr() as *mut c_void,
+                cache.cos.as_ptr() as _, cache.sin.as_ptr() as _,
+                pos_gpu.as_ptr() as _,
+                num_tokens as i32, num_heads as i32, head_dim as i32,
+                std::ptr::null_mut(),
+            ),
+            _ => panic!("unsupported dtype for rope"),
+        }
+    }
+    xserv_cuda::device::synchronize().unwrap();
+}
--- a/crates/xserv-kernels/src/softmax.rs
+++ b/crates/xserv-kernels/src/softmax.rs
@@ -0,0 +1,34 @@
+use std::ffi::c_void;
+use xserv_tensor::{DType, Device, Tensor};
+
+unsafe extern "C" {
+    fn launch_softmax_f32(x: *const c_void, out: *mut c_void, rows: i32, cols: i32, stream: *mut c_void);
+    fn launch_softmax_bf16(x: *const c_void, out: *mut c_void, rows: i32, cols: i32, stream: *mut c_void);
+}
+
+/// Softmax along the last dimension.
+pub fn softmax(x: &Tensor) -> Tensor {
+    assert!(x.ndim() >= 1);
+    assert!(x.is_contiguous());
+    assert!(matches!(x.device(), Device::Cuda(_)));
+
+    let cols = *x.shape().last().unwrap();
+    let rows = x.numel() / cols;
+    let out = Tensor::zeros(x.shape(), x.dtype(), x.device());
+
+    unsafe {
+        match x.dtype() {
+            DType::F32 => launch_softmax_f32(
+                x.data_ptr() as _, out.data_ptr() as *mut c_void,
+                rows as i32, cols as i32, std::ptr::null_mut(),
+            ),
+            DType::BF16 => launch_softmax_bf16(
+                x.data_ptr() as _, out.data_ptr() as *mut c_void,
+                rows as i32, cols as i32, std::ptr::null_mut(),
+            ),
+            _ => panic!("unsupported dtype for softmax"),
+        }
+    }
+    xserv_cuda::device::synchronize().unwrap();
+    out
+}
--- a/crates/xserv-kernels/tests/attention_test.rs
+++ b/crates/xserv-kernels/tests/attention_test.rs
@@ -0,0 +1,187 @@
+use xserv_kernels::*;
+use xserv_tensor::{Device, Tensor};
+
+fn init() { xserv_cuda::device::set_device(0).unwrap(); }
+
+fn cpu_attention(q: &[f32], k: &[f32], v: &[f32],
+                 batch: usize, heads: usize, q_len: usize, kv_len: usize, head_dim: usize,
+                 causal: bool) -> Vec<f32> {
+    let mut out = vec![0.0f32; batch * heads * q_len * head_dim];
+    let scale = 1.0 / (head_dim as f32).sqrt();
+
+    for b in 0..batch {
+        for h in 0..heads {
+            // scores = Q @ K^T, scaled
+            let mut scores = vec![0.0f32; q_len * kv_len];
+            for i in 0..q_len {
+                for j in 0..kv_len {
+                    let mut s = 0.0f32;
+                    for d in 0..head_dim {
+                        let qi = q[((b * heads + h) * q_len + i) * head_dim + d];
+                        let ki = k[((b * heads + h) * kv_len + j) * head_dim + d];
+                        s += qi * ki;
+                    }
+                    scores[i * kv_len + j] = s * scale;
+                }
+            }
+            // causal mask
+            if causal {
+                let offset = kv_len - q_len;
+                for i in 0..q_len {
+                    for j in 0..kv_len {
+                        if j > i + offset {
+                            scores[i * kv_len + j] = f32::NEG_INFINITY;
+                        }
+                    }
+                }
+            }
+            // softmax per row
+            for i in 0..q_len {
+                let row = &mut scores[i * kv_len..(i + 1) * kv_len];
+                let max = row.iter().cloned().fold(f32::NEG_INFINITY, f32::max);
+                let mut sum = 0.0f32;
+                for v in row.iter_mut() {
+                    *v = (*v - max).exp();
+                    sum += *v;
+                }
+                for v in row.iter_mut() {
+                    *v /= sum;
+                }
+            }
+            // output = weights @ V
+            for i in 0..q_len {
+                for d in 0..head_dim {
+                    let mut s = 0.0f32;
+                    for j in 0..kv_len {
+                        let w = scores[i * kv_len + j];
+                        let vi = v[((b * heads + h) * kv_len + j) * head_dim + d];
+                        s += w * vi;
+                    }
+                    out[((b * heads + h) * q_len + i) * head_dim + d] = s;
+                }
+            }
+        }
+    }
+    out
+}
+
+fn check_close(a: &[f32], b: &[f32], atol: f32, name: &str) {
+    assert_eq!(a.len(), b.len(), "{name}: length mismatch");
+    let mut max_err = 0.0f32;
+    for (i, (x, y)) in a.iter().zip(b).enumerate() {
+        let err = (x - y).abs();
+        if err > max_err { max_err = err; }
+        assert!(err <= atol, "{name}: mismatch at [{i}]: got {x}, expected {y}, err {err}");
+    }
+    println!("{name}: max_err = {max_err:.6e}");
+}
+
+fn make_data(n: usize) -> Vec<f32> {
+    (0..n).map(|i| ((i % 17) as f32 - 8.0) * 0.05).collect()
+}
+
+#[test]
+fn test_batched_matmul() {
+    init();
+    let batch = 4;
+    let heads = 8;
+    let m = 32;
+    let k = 64;
+    let n = 32;
+
+    let a_data = make_data(batch * heads * m * k);
+    let b_data = make_data(batch * heads * k * n);
+
+    let a = Tensor::from_slice(&a_data, &[batch, heads, m, k]).to_device(Device::Cuda(0));
+    let b = Tensor::from_slice(&b_data, &[batch, heads, k, n]).to_device(Device::Cuda(0));
+    let c = batched_matmul(&a, &b).to_device(Device::Cpu);
+
+    assert_eq!(c.shape(), &[batch, heads, m, n]);
+
+    // Verify one batch element
+    let a_cpu = &a_data[0..m * k];
+    let b_cpu = &b_data[0..k * n];
+    let mut expected = vec![0.0f32; m * n];
+    for i in 0..m {
+        for j in 0..n {
+            let mut s = 0.0f32;
+            for kk in 0..k { s += a_cpu[i * k + kk] * b_cpu[kk * n + j]; }
+            expected[i * n + j] = s;
+        }
+    }
+    let result = c.as_slice::<f32>();
+    check_close(&result[0..m * n], &expected, 1e-3, "batched_matmul[0]");
+}
+
+#[test]
+fn test_attention_no_causal() {
+    init();
+    let b = 1; let h = 2; let s = 8; let d = 16;
+    let q_data = make_data(b * h * s * d);
+    let k_data = make_data(b * h * s * d);
+    let v_data = make_data(b * h * s * d);
+    let expected = cpu_attention(&q_data, &k_data, &v_data, b, h, s, s, d, false);
+
+    let q = Tensor::from_slice(&q_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let k = Tensor::from_slice(&k_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let v = Tensor::from_slice(&v_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let out = attention(&q, &k, &v, false).to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-4, "attention_no_causal");
+}
+
+#[test]
+fn test_attention_causal() {
+    init();
+    let b = 1; let h = 2; let s = 16; let d = 32;
+    let q_data = make_data(b * h * s * d);
+    let k_data = make_data(b * h * s * d);
+    let v_data = make_data(b * h * s * d);
+    let expected = cpu_attention(&q_data, &k_data, &v_data, b, h, s, s, d, true);
+
+    let q = Tensor::from_slice(&q_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let k = Tensor::from_slice(&k_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let v = Tensor::from_slice(&v_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let out = attention(&q, &k, &v, true).to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-3, "attention_causal");
+}
+
+#[test]
+fn test_attention_causal_larger() {
+    init();
+    let b = 2; let h = 4; let s = 64; let d = 64;
+    let q_data = make_data(b * h * s * d);
+    let k_data = make_data(b * h * s * d);
+    let v_data = make_data(b * h * s * d);
+    let expected = cpu_attention(&q_data, &k_data, &v_data, b, h, s, s, d, true);
+
+    let q = Tensor::from_slice(&q_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let k = Tensor::from_slice(&k_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let v = Tensor::from_slice(&v_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let out = attention(&q, &k, &v, true).to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-2, "attention_causal_larger");
+}
+
+#[test]
+fn test_attention_causal_first_row_sees_only_first_token() {
+    init();
+    let b = 1; let h = 1; let s = 4; let d = 8;
+    let q_data = make_data(b * h * s * d);
+    let k_data = make_data(b * h * s * d);
+    let v_data: Vec<f32> = (0..s * d).map(|i| {
+        if i < d { 1.0 } else { 0.0 }  // only first V row is nonzero
+    }).collect();
+
+    let q = Tensor::from_slice(&q_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let k = Tensor::from_slice(&k_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let v = Tensor::from_slice(&v_data, &[b, h, s, d]).to_device(Device::Cuda(0));
+    let out = attention(&q, &k, &v, true).to_device(Device::Cpu);
+
+    // First row (position 0) with causal mask can only see position 0.
+    // So attention weight for position 0 is 1.0 for token 0 only.
+    // output[0] should be exactly V[0] = [1, 1, 1, ...1]
+    let result = out.as_slice::<f32>();
+    for i in 0..d {
+        assert!((result[i] - 1.0).abs() < 1e-5,
+            "first row should equal V[0], got {} at dim {}", result[i], i);
+    }
+}
--- a/crates/xserv-kernels/tests/ops_test.rs
+++ b/crates/xserv-kernels/tests/ops_test.rs
@@ -0,0 +1,302 @@
+use half::bf16;
+use xserv_kernels::*;
+use xserv_tensor::{Device, Tensor};
+
+fn init() { xserv_cuda::device::set_device(0).unwrap(); }
+
+// --- CPU reference implementations ---
+
+fn cpu_rmsnorm(x: &[f32], gamma: &[f32], eps: f32, hidden: usize) -> Vec<f32> {
+    let rows = x.len() / hidden;
+    let mut out = vec![0.0f32; x.len()];
+    for r in 0..rows {
+        let row = &x[r * hidden..(r + 1) * hidden];
+        let sum_sq: f32 = row.iter().map(|v| v * v).sum();
+        let rms_inv = 1.0 / (sum_sq / hidden as f32 + eps).sqrt();
+        for i in 0..hidden {
+            out[r * hidden + i] = row[i] * rms_inv * gamma[i];
+        }
+    }
+    out
+}
+
+fn cpu_layernorm(x: &[f32], gamma: &[f32], beta: &[f32], eps: f32, hidden: usize) -> Vec<f32> {
+    let rows = x.len() / hidden;
+    let mut out = vec![0.0f32; x.len()];
+    for r in 0..rows {
+        let row = &x[r * hidden..(r + 1) * hidden];
+        let mean: f32 = row.iter().sum::<f32>() / hidden as f32;
+        let var: f32 = row.iter().map(|v| (v - mean) * (v - mean)).sum::<f32>() / hidden as f32;
+        let inv_std = 1.0 / (var + eps).sqrt();
+        for i in 0..hidden {
+            out[r * hidden + i] = gamma[i] * (row[i] - mean) * inv_std + beta[i];
+        }
+    }
+    out
+}
+
+fn cpu_gelu(x: &[f32]) -> Vec<f32> {
+    let sqrt_2_over_pi = 0.7978845608f32;
+    x.iter().map(|&v| {
+        let inner = sqrt_2_over_pi * (v + 0.044715 * v * v * v);
+        0.5 * v * (1.0 + inner.tanh())
+    }).collect()
+}
+
+fn cpu_silu(x: &[f32]) -> Vec<f32> {
+    x.iter().map(|&v| v / (1.0 + (-v).exp())).collect()
+}
+
+fn cpu_softmax(x: &[f32], cols: usize) -> Vec<f32> {
+    let rows = x.len() / cols;
+    let mut out = vec![0.0f32; x.len()];
+    for r in 0..rows {
+        let row = &x[r * cols..(r + 1) * cols];
+        let max = row.iter().cloned().fold(f32::NEG_INFINITY, f32::max);
+        let exps: Vec<f32> = row.iter().map(|v| (v - max).exp()).collect();
+        let sum: f32 = exps.iter().sum();
+        for i in 0..cols {
+            out[r * cols + i] = exps[i] / sum;
+        }
+    }
+    out
+}
+
+fn cpu_rope(x: &mut [f32], positions: &[u32], num_heads: usize, head_dim: usize, theta: f32) {
+    let half_dim = head_dim / 2;
+    let num_tokens = positions.len();
+    for t in 0..num_tokens {
+        let pos = positions[t] as f32;
+        for h in 0..num_heads {
+            for i in 0..half_dim {
+                let freq = 1.0 / theta.powf(2.0 * i as f32 / head_dim as f32);
+                let angle = pos * freq;
+                let cos_val = angle.cos();
+                let sin_val = angle.sin();
+                let base = (t * num_heads + h) * head_dim;
+                let x0 = x[base + 2 * i];
+                let x1 = x[base + 2 * i + 1];
+                x[base + 2 * i]     = x0 * cos_val - x1 * sin_val;
+                x[base + 2 * i + 1] = x0 * sin_val + x1 * cos_val;
+            }
+        }
+    }
+}
+
+fn check_close(result: &[f32], expected: &[f32], atol: f32, name: &str) {
+    assert_eq!(result.len(), expected.len(), "{name}: length mismatch");
+    let mut max_err = 0.0f32;
+    for (i, (r, e)) in result.iter().zip(expected).enumerate() {
+        let err = (r - e).abs();
+        if err > max_err { max_err = err; }
+        assert!(err <= atol, "{name}: mismatch at [{i}]: got {r}, expected {e}, err {err}");
+    }
+    println!("{name}: max_err = {max_err:.6e}");
+}
+
+fn make_data(n: usize) -> Vec<f32> {
+    (0..n).map(|i| ((i % 17) as f32 - 8.0) * 0.1).collect()
+}
+
+// === RMSNorm ===
+
+#[test]
+fn test_rmsnorm_f32() {
+    init();
+    let hidden = 768;
+    let rows = 4;
+    let x_data = make_data(rows * hidden);
+    let gamma_data: Vec<f32> = (0..hidden).map(|i| 0.5 + (i % 3) as f32 * 0.2).collect();
+    let expected = cpu_rmsnorm(&x_data, &gamma_data, 1e-5, hidden);
+
+    let x = Tensor::from_slice(&x_data, &[rows, hidden]).to_device(Device::Cuda(0));
+    let gamma = Tensor::from_slice(&gamma_data, &[hidden]).to_device(Device::Cuda(0));
+    let out = rmsnorm(&x, &gamma, 1e-5).to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-4, "rmsnorm_f32");
+}
+
+#[test]
+fn test_rmsnorm_bf16() {
+    init();
+    let hidden = 768;
+    let rows = 4;
+    let x_f32 = make_data(rows * hidden);
+    let gamma_f32: Vec<f32> = (0..hidden).map(|i| 0.5 + (i % 3) as f32 * 0.2).collect();
+    let expected = cpu_rmsnorm(&x_f32, &gamma_f32, 1e-5, hidden);
+
+    let x_bf16: Vec<bf16> = x_f32.iter().map(|&v| bf16::from_f32(v)).collect();
+    let gamma_bf16: Vec<bf16> = gamma_f32.iter().map(|&v| bf16::from_f32(v)).collect();
+    let x = Tensor::from_slice(&x_bf16, &[rows, hidden]).to_device(Device::Cuda(0));
+    let gamma = Tensor::from_slice(&gamma_bf16, &[hidden]).to_device(Device::Cuda(0));
+    let out = rmsnorm(&x, &gamma, 1e-5).to_device(Device::Cpu);
+
+    let result: Vec<f32> = out.as_slice::<bf16>().iter().map(|v| v.to_f32()).collect();
+    check_close(&result, &expected, 0.05, "rmsnorm_bf16");
+}
+
+// === LayerNorm ===
+
+#[test]
+fn test_layernorm_f32() {
+    init();
+    let hidden = 768;
+    let rows = 4;
+    let x_data = make_data(rows * hidden);
+    let gamma_data: Vec<f32> = (0..hidden).map(|i| 0.8 + (i % 5) as f32 * 0.1).collect();
+    let beta_data: Vec<f32> = (0..hidden).map(|i| ((i % 7) as f32 - 3.0) * 0.01).collect();
+    let expected = cpu_layernorm(&x_data, &gamma_data, &beta_data, 1e-5, hidden);
+
+    let x = Tensor::from_slice(&x_data, &[rows, hidden]).to_device(Device::Cuda(0));
+    let gamma = Tensor::from_slice(&gamma_data, &[hidden]).to_device(Device::Cuda(0));
+    let beta = Tensor::from_slice(&beta_data, &[hidden]).to_device(Device::Cuda(0));
+    let out = layernorm(&x, &gamma, &beta, 1e-5).to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-4, "layernorm_f32");
+}
+
+// === GELU ===
+
+#[test]
+fn test_gelu_f32() {
+    init();
+    let data = make_data(10000);
+    let expected = cpu_gelu(&data);
+    let x = Tensor::from_slice(&data, &[10000]).to_device(Device::Cuda(0));
+    let out = gelu(&x).to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-5, "gelu_f32");
+}
+
+#[test]
+fn test_gelu_bf16() {
+    init();
+    let data_f32 = make_data(10000);
+    let expected = cpu_gelu(&data_f32);
+    let data_bf16: Vec<bf16> = data_f32.iter().map(|&v| bf16::from_f32(v)).collect();
+    let x = Tensor::from_slice(&data_bf16, &[10000]).to_device(Device::Cuda(0));
+    let out = gelu(&x).to_device(Device::Cpu);
+    let result: Vec<f32> = out.as_slice::<bf16>().iter().map(|v| v.to_f32()).collect();
+    check_close(&result, &expected, 0.02, "gelu_bf16");
+}
+
+// === SiLU ===
+
+#[test]
+fn test_silu_f32() {
+    init();
+    let data = make_data(10000);
+    let expected = cpu_silu(&data);
+    let x = Tensor::from_slice(&data, &[10000]).to_device(Device::Cuda(0));
+    let out = silu(&x).to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-5, "silu_f32");
+}
+
+// === Softmax ===
+
+#[test]
+fn test_softmax_f32() {
+    init();
+    let rows = 8;
+    let cols = 256;
+    let data = make_data(rows * cols);
+    let expected = cpu_softmax(&data, cols);
+    let x = Tensor::from_slice(&data, &[rows, cols]).to_device(Device::Cuda(0));
+    let out = softmax(&x).to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-5, "softmax_f32");
+}
+
+#[test]
+fn test_softmax_sum_to_one() {
+    init();
+    let rows = 4;
+    let cols = 2048;
+    let data: Vec<f32> = (0..rows * cols).map(|i| ((i % 31) as f32 - 15.0) * 0.5).collect();
+    let x = Tensor::from_slice(&data, &[rows, cols]).to_device(Device::Cuda(0));
+    let out = softmax(&x).to_device(Device::Cpu);
+    let result = out.as_slice::<f32>();
+    for r in 0..rows {
+        let row_sum: f32 = result[r * cols..(r + 1) * cols].iter().sum();
+        assert!((row_sum - 1.0).abs() < 1e-5, "softmax row {r} sum = {row_sum}");
+    }
+}
+
+#[test]
+fn test_softmax_large_values() {
+    init();
+    let data = vec![1000.0f32, 1001.0, 999.0, 1000.5];
+    let expected = cpu_softmax(&data, 4);
+    let x = Tensor::from_slice(&data, &[1, 4]).to_device(Device::Cuda(0));
+    let out = softmax(&x).to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-5, "softmax_large");
+}
+
+// === Embedding ===
+
+#[test]
+fn test_embedding_f32() {
+    init();
+    let vocab_size = 100;
+    let hidden = 64;
+    let table_data: Vec<f32> = (0..vocab_size * hidden).map(|i| i as f32 * 0.01).collect();
+    let token_ids: Vec<u32> = vec![0, 5, 99, 42, 1];
+
+    let table = Tensor::from_slice(&table_data, &[vocab_size, hidden]).to_device(Device::Cuda(0));
+    let out = embedding(&table, &token_ids).to_device(Device::Cpu);
+
+    assert_eq!(out.shape(), &[5, hidden]);
+    let result = out.as_slice::<f32>();
+    for (seq_idx, &tid) in token_ids.iter().enumerate() {
+        for i in 0..hidden {
+            let expected = table_data[tid as usize * hidden + i];
+            let got = result[seq_idx * hidden + i];
+            assert!((got - expected).abs() < 1e-6,
+                "embedding mismatch at [{seq_idx},{i}]: got {got}, expected {expected}");
+        }
+    }
+}
+
+// === RoPE ===
+
+#[test]
+fn test_rope_f32() {
+    init();
+    let num_tokens = 4;
+    let num_heads = 2;
+    let head_dim = 8;
+    let theta = 10000.0f32;
+    let positions: Vec<u32> = vec![0, 1, 2, 3];
+
+    let x_data: Vec<f32> = (0..num_tokens * num_heads * head_dim)
+        .map(|i| ((i % 13) as f32 - 6.0) * 0.1)
+        .collect();
+    let mut expected = x_data.clone();
+    cpu_rope(&mut expected, &positions, num_heads, head_dim, theta);
+
+    let x = Tensor::from_slice(&x_data, &[num_tokens, num_heads, head_dim])
+        .to_device(Device::Cuda(0));
+    let cache = RopeCache::new(64, head_dim, theta);
+    rope_inplace(&x, &cache, &positions);
+
+    let out = x.to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &expected, 1e-4, "rope_f32");
+}
+
+#[test]
+fn test_rope_position_0_identity() {
+    init();
+    // At position 0, all angles are 0, so cos=1, sin=0 → identity transform
+    let num_tokens = 1;
+    let num_heads = 2;
+    let head_dim = 8;
+    let positions: Vec<u32> = vec![0];
+
+    let x_data: Vec<f32> = (0..num_tokens * num_heads * head_dim)
+        .map(|i| (i as f32 + 1.0) * 0.1)
+        .collect();
+
+    let x = Tensor::from_slice(&x_data, &[num_tokens, num_heads, head_dim])
+        .to_device(Device::Cuda(0));
+    let cache = RopeCache::new(64, head_dim, 10000.0);
+    rope_inplace(&x, &cache, &positions);
+
+    let out = x.to_device(Device::Cpu);
+    check_close(out.as_slice::<f32>(), &x_data, 1e-6, "rope_pos0");
+}
--- a/crates/xserv-model/Cargo.toml
+++ b/crates/xserv-model/Cargo.toml
@@ -0,0 +1,14 @@
+[package]
+name = "xserv-model"
+version.workspace = true
+edition.workspace = true
+
+[dependencies]
+xserv-cuda = { path = "../xserv-cuda" }
+xserv-tensor = { path = "../xserv-tensor" }
+xserv-kernels = { path = "../xserv-kernels" }
+xserv-tokenizer = { path = "../xserv-tokenizer" }
+half.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+safetensors.workspace = true
--- a/crates/xserv-model/src/bin/xserv-cli.rs
+++ b/crates/xserv-model/src/bin/xserv-cli.rs
@@ -0,0 +1,78 @@
+use std::io::{self, Write};
+use std::path::PathBuf;
+use xserv_model::{GPT2, ModelConfig};
+use xserv_model::loader;
+use xserv_model::gpt2::sample_greedy;
+use xserv_tokenizer::Tokenizer;
+use xserv_tensor::Device;
+
+fn main() {
+    let args: Vec<String> = std::env::args().collect();
+    if args.len() < 2 {
+        eprintln!("Usage: xserv-cli <model-dir> [--max-tokens N]");
+        eprintln!("  model-dir: path to HF model directory (containing model.safetensors, config.json, tokenizer.json)");
+        std::process::exit(1);
+    }
+
+    let model_dir = PathBuf::from(&args[1]);
+    let max_tokens: usize = args.iter()
+        .position(|a| a == "--max-tokens")
+        .and_then(|i| args.get(i + 1))
+        .and_then(|s| s.parse().ok())
+        .unwrap_or(100);
+
+    xserv_cuda::device::set_device(0).unwrap();
+    let info = xserv_cuda::device::device_info(0).unwrap();
+    eprintln!("GPU: {} ({} MB free)", info.name, info.free_memory / 1024 / 1024);
+
+    // Load config
+    let config = ModelConfig::from_file(&model_dir.join("config.json"));
+    eprintln!("Model: {:?}, layers={}, hidden={}, heads={}, vocab={}",
+        config.model_type, config.num_layers(), config.hidden(),
+        config.num_heads(), config.vocab_size);
+
+    // Load weights
+    eprintln!("Loading weights...");
+    let weights = loader::load_model_dir(&model_dir, Device::Cuda(0));
+    eprintln!("Loaded {} tensors", weights.len());
+
+    // GPT-2 uses weight names without "model." prefix
+    let model = GPT2::from_weights(config, weights);
+
+    // Load tokenizer
+    let tokenizer = Tokenizer::from_file(&model_dir.join("tokenizer.json"));
+    eprintln!("Tokenizer loaded (vocab_size={})", tokenizer.vocab_size());
+    eprintln!("Ready.\n");
+
+    // Interactive loop
+    loop {
+        print!("xserv> ");
+        io::stdout().flush().unwrap();
+        let mut input = String::new();
+        if io::stdin().read_line(&mut input).unwrap() == 0 {
+            break;
+        }
+        let input = input.trim();
+        if input.is_empty() { continue; }
+        if input == "quit" || input == "exit" { break; }
+
+        let mut token_ids = tokenizer.encode(input);
+        print!("{input}");
+        io::stdout().flush().unwrap();
+
+        for _ in 0..max_tokens {
+            let logits = model.forward(&token_ids);
+            let next = sample_greedy(&logits);
+            token_ids.push(next);
+
+            let text = tokenizer.decode(&[next]);
+            print!("{text}");
+            io::stdout().flush().unwrap();
+
+            if tokenizer.eos_token_id() == Some(next) {
+                break;
+            }
+        }
+        println!();
+    }
+}
--- a/crates/xserv-model/src/config.rs
+++ b/crates/xserv-model/src/config.rs
@@ -0,0 +1,96 @@
+use serde::Deserialize;
+use std::path::Path;
+
+#[derive(Debug, Clone, Deserialize)]
+pub struct ModelConfig {
+    pub architectures: Option<Vec<String>>,
+    pub model_type: Option<String>,
+
+    // Modern HF naming
+    #[serde(default)]
+    pub hidden_size: Option<usize>,
+    #[serde(default)]
+    pub intermediate_size: Option<usize>,
+    #[serde(default)]
+    pub num_attention_heads: Option<usize>,
+    #[serde(default)]
+    pub num_key_value_heads: Option<usize>,
+    #[serde(default)]
+    pub num_hidden_layers: Option<usize>,
+    pub vocab_size: usize,
+    #[serde(default)]
+    pub max_position_embeddings: Option<usize>,
+
+    // GPT-2 naming
+    #[serde(default)]
+    pub n_embd: Option<usize>,
+    #[serde(default)]
+    pub n_head: Option<usize>,
+    #[serde(default)]
+    pub n_layer: Option<usize>,
+    #[serde(default)]
+    pub n_positions: Option<usize>,
+    #[serde(default)]
+    pub n_inner: Option<usize>,
+
+    // Normalization
+    #[serde(default)]
+    pub layer_norm_eps: Option<f64>,
+    #[serde(default)]
+    pub layer_norm_epsilon: Option<f64>,
+    #[serde(default)]
+    pub rms_norm_eps: Option<f64>,
+
+    // Other
+    #[serde(default)]
+    pub rope_theta: Option<f64>,
+    #[serde(default)]
+    pub tie_word_embeddings: Option<bool>,
+}
+
+impl ModelConfig {
+    pub fn from_file(path: &Path) -> Self {
+        let data = std::fs::read_to_string(path)
+            .unwrap_or_else(|e| panic!("failed to read {}: {e}", path.display()));
+        serde_json::from_str(&data)
+            .unwrap_or_else(|e| panic!("failed to parse {}: {e}", path.display()))
+    }
+
+    pub fn hidden(&self) -> usize {
+        self.hidden_size.or(self.n_embd).expect("hidden_size or n_embd required")
+    }
+
+    pub fn num_heads(&self) -> usize {
+        self.num_attention_heads.or(self.n_head).expect("num_attention_heads or n_head required")
+    }
+
+    pub fn num_layers(&self) -> usize {
+        self.num_hidden_layers.or(self.n_layer).expect("num_hidden_layers or n_layer required")
+    }
+
+    pub fn max_seq_len(&self) -> usize {
+        self.max_position_embeddings.or(self.n_positions).unwrap_or(2048)
+    }
+
+    pub fn ffn_hidden(&self) -> usize {
+        self.intermediate_size.or(self.n_inner).unwrap_or(self.hidden() * 4)
+    }
+
+    pub fn num_kv_heads(&self) -> usize {
+        self.num_key_value_heads.unwrap_or(self.num_heads())
+    }
+
+    pub fn head_dim(&self) -> usize {
+        self.hidden() / self.num_heads()
+    }
+
+    pub fn ln_eps(&self) -> f32 {
+        self.layer_norm_eps
+            .or(self.layer_norm_epsilon)
+            .unwrap_or(1e-5) as f32
+    }
+
+    pub fn tied_embeddings(&self) -> bool {
+        self.tie_word_embeddings.unwrap_or(true)
+    }
+}
--- a/crates/xserv-model/src/gpt2.rs
+++ b/crates/xserv-model/src/gpt2.rs
@@ -0,0 +1,224 @@
+use std::collections::HashMap;
+use xserv_kernels::*;
+use xserv_tensor::{DType, Device, Tensor};
+
+use crate::config::ModelConfig;
+
+pub struct GPT2 {
+    pub config: ModelConfig,
+    wte: Tensor,       // [vocab_size, hidden]
+    wpe: Tensor,       // [max_pos, hidden]
+    layers: Vec<GPT2Block>,
+    ln_f_g: Tensor,    // [hidden]
+    ln_f_b: Tensor,    // [hidden]
+}
+
+struct GPT2Block {
+    ln_1_g: Tensor,
+    ln_1_b: Tensor,
+    // Attention: combined QKV weight + bias, output weight + bias
+    attn_qkv_w: Tensor, // [hidden, 3*hidden]
+    attn_qkv_b: Tensor, // [3*hidden]
+    attn_out_w: Tensor,  // [hidden, hidden]
+    attn_out_b: Tensor,  // [hidden]
+    ln_2_g: Tensor,
+    ln_2_b: Tensor,
+    mlp_fc_w: Tensor,   // [hidden, 4*hidden]
+    mlp_fc_b: Tensor,   // [4*hidden]
+    mlp_proj_w: Tensor,  // [4*hidden, hidden]
+    mlp_proj_b: Tensor,  // [hidden]
+}
+
+impl GPT2 {
+    pub fn from_weights(config: ModelConfig, mut w: HashMap<String, Tensor>) -> Self {
+        let take = |w: &mut HashMap<String, Tensor>, name: &str| -> Tensor {
+            w.remove(name).unwrap_or_else(|| panic!("missing weight: {name}"))
+        };
+
+        let wte = take(&mut w, "wte.weight");
+        let wpe = take(&mut w, "wpe.weight");
+        let ln_f_g = take(&mut w, "ln_f.weight");
+        let ln_f_b = take(&mut w, "ln_f.bias");
+
+        let num_layers = config.num_layers();
+        let mut layers = Vec::with_capacity(num_layers);
+        for i in 0..num_layers {
+            let p = format!("h.{i}");
+            layers.push(GPT2Block {
+                ln_1_g: take(&mut w, &format!("{p}.ln_1.weight")),
+                ln_1_b: take(&mut w, &format!("{p}.ln_1.bias")),
+                attn_qkv_w: take(&mut w, &format!("{p}.attn.c_attn.weight")),
+                attn_qkv_b: take(&mut w, &format!("{p}.attn.c_attn.bias")),
+                attn_out_w: take(&mut w, &format!("{p}.attn.c_proj.weight")),
+                attn_out_b: take(&mut w, &format!("{p}.attn.c_proj.bias")),
+                ln_2_g: take(&mut w, &format!("{p}.ln_2.weight")),
+                ln_2_b: take(&mut w, &format!("{p}.ln_2.bias")),
+                mlp_fc_w: take(&mut w, &format!("{p}.mlp.c_fc.weight")),
+                mlp_fc_b: take(&mut w, &format!("{p}.mlp.c_fc.bias")),
+                mlp_proj_w: take(&mut w, &format!("{p}.mlp.c_proj.weight")),
+                mlp_proj_b: take(&mut w, &format!("{p}.mlp.c_proj.bias")),
+            });
+        }
+
+        Self { config, wte, wpe, layers, ln_f_g, ln_f_b }
+    }
+
+    /// Full forward pass, returns logits [seq_len, vocab_size].
+    pub fn forward(&self, token_ids: &[u32]) -> Tensor {
+        let seq_len = token_ids.len();
+        let hidden = self.config.hidden();
+        let num_heads = self.config.num_heads();
+        let head_dim = self.config.head_dim();
+
+        // Token + position embedding
+        let tok_emb = embedding(&self.wte, token_ids);
+        let pos_ids: Vec<u32> = (0..seq_len as u32).collect();
+        let pos_emb = embedding(&self.wpe, &pos_ids);
+        let mut x = add_tensors(&tok_emb, &pos_emb);
+
+        // Transformer layers
+        for layer in &self.layers {
+            // Pre-LN attention
+            let residual = x.clone();
+            let normed = layernorm(&x, &layer.ln_1_g, &layer.ln_1_b, self.config.ln_eps());
+
+            // QKV projection: [S, H] @ [H, 3H] + [3H] → [S, 3H]
+            let qkv = linear(&normed, &layer.attn_qkv_w, Some(&layer.attn_qkv_b));
+            // Split into Q, K, V and reshape for multi-head
+            let (q, k, v) = split_qkv(&qkv, num_heads, head_dim, seq_len);
+            // Attention: [1, H, S, D]
+            let attn_out = attention(&q, &k, &v, true);
+            // Merge heads: [1, H, S, D] → [S, hidden]
+            let attn_out = merge_heads(&attn_out, seq_len, hidden);
+            // Output projection
+            let attn_out = linear(&attn_out, &layer.attn_out_w, Some(&layer.attn_out_b));
+            x = add_tensors(&residual, &attn_out);
+
+            // Pre-LN MLP
+            let residual = x.clone();
+            let normed = layernorm(&x, &layer.ln_2_g, &layer.ln_2_b, self.config.ln_eps());
+            let fc = linear(&normed, &layer.mlp_fc_w, Some(&layer.mlp_fc_b));
+            let activated = gelu(&fc);
+            let proj = linear(&activated, &layer.mlp_proj_w, Some(&layer.mlp_proj_b));
+            x = add_tensors(&residual, &proj);
+        }
+
+        // Final layer norm
+        let x = layernorm(&x, &self.ln_f_g, &self.ln_f_b, self.config.ln_eps());
+
+        // LM head (tied with wte): [S, H] @ [H, V] → [S, V]
+        // wte is [V, H], so we need wte^T
+        let lm_head = self.wte.transpose(0, 1).contiguous();
+        matmul_2d(&x, &lm_head)
+    }
+}
+
+// --- Helper ops ---
+
+fn linear(x: &Tensor, weight: &Tensor, bias: Option<&Tensor>) -> Tensor {
+    // GPT-2 stores weights as [in, out] (not transposed), so x @ w
+    let out = matmul_2d(x, weight);
+    if let Some(b) = bias {
+        add_bias(&out, b)
+    } else {
+        out
+    }
+}
+
+fn matmul_2d(a: &Tensor, b: &Tensor) -> Tensor {
+    // a: [S, K], b: [K, N] → [S, N]
+    assert_eq!(a.ndim(), 2);
+    assert_eq!(b.ndim(), 2);
+    matmul(a, b, GemmBackend::CuBlas)
+}
+
+fn add_tensors(a: &Tensor, b: &Tensor) -> Tensor {
+    // Element-wise add on GPU via a simple approach: scale(a, 1.0) + scale(b, 1.0)
+    // TODO: proper add kernel. For now, go through CPU.
+    assert_eq!(a.shape(), b.shape());
+    assert_eq!(a.dtype(), DType::F32);
+    let a_cpu = a.to_device(Device::Cpu);
+    let b_cpu = b.to_device(Device::Cpu);
+    let a_data = a_cpu.as_slice::<f32>();
+    let b_data = b_cpu.as_slice::<f32>();
+    let sum: Vec<f32> = a_data.iter().zip(b_data).map(|(x, y)| x + y).collect();
+    Tensor::from_slice(&sum, a.shape()).to_device(a.device())
+}
+
+fn add_bias(x: &Tensor, bias: &Tensor) -> Tensor {
+    // x: [S, N], bias: [N] → broadcast add
+    assert_eq!(x.ndim(), 2);
+    assert_eq!(bias.ndim(), 1);
+    assert_eq!(x.shape()[1], bias.shape()[0]);
+    let x_cpu = x.to_device(Device::Cpu);
+    let b_cpu = bias.to_device(Device::Cpu);
+    let x_data = x_cpu.as_slice::<f32>();
+    let b_data = b_cpu.as_slice::<f32>();
+    let n = bias.shape()[0];
+    let result: Vec<f32> = x_data.iter().enumerate().map(|(i, &v)| v + b_data[i % n]).collect();
+    Tensor::from_slice(&result, x.shape()).to_device(x.device())
+}
+
+fn split_qkv(qkv: &Tensor, num_heads: usize, head_dim: usize, seq_len: usize) -> (Tensor, Tensor, Tensor) {
+    // qkv: [S, 3*H] → Q, K, V each [1, num_heads, S, head_dim]
+    let hidden = num_heads * head_dim;
+    let qkv_cpu = qkv.to_device(Device::Cpu);
+    let data = qkv_cpu.as_slice::<f32>();
+
+    // Split into Q, K, V and directly write in [1, num_heads, S, head_dim] layout
+    let mut q_data = vec![0.0f32; num_heads * seq_len * head_dim];
+    let mut k_data = vec![0.0f32; num_heads * seq_len * head_dim];
+    let mut v_data = vec![0.0f32; num_heads * seq_len * head_dim];
+
+    for s in 0..seq_len {
+        let row = &data[s * 3 * hidden..(s + 1) * 3 * hidden];
+        for h in 0..num_heads {
+            let src_off = h * head_dim;
+            let dst_off = (h * seq_len + s) * head_dim;
+            q_data[dst_off..dst_off + head_dim].copy_from_slice(&row[src_off..src_off + head_dim]);
+            k_data[dst_off..dst_off + head_dim].copy_from_slice(&row[hidden + src_off..hidden + src_off + head_dim]);
+            v_data[dst_off..dst_off + head_dim].copy_from_slice(&row[2 * hidden + src_off..2 * hidden + src_off + head_dim]);
+        }
+    }
+
+    let device = qkv.device();
+    let q = Tensor::from_slice(&q_data, &[1, num_heads, seq_len, head_dim]).to_device(device);
+    let k = Tensor::from_slice(&k_data, &[1, num_heads, seq_len, head_dim]).to_device(device);
+    let v = Tensor::from_slice(&v_data, &[1, num_heads, seq_len, head_dim]).to_device(device);
+    (q, k, v)
+}
+
+fn merge_heads(x: &Tensor, seq_len: usize, hidden: usize) -> Tensor {
+    // [1, num_heads, S, head_dim] → [S, hidden]
+    let num_heads = x.shape()[1];
+    let head_dim = x.shape()[3];
+    let x_cpu = x.to_device(Device::Cpu);
+    let src = x_cpu.as_slice::<f32>();
+
+    // src layout: [1][num_heads][seq_len][head_dim]
+    // dst layout: [seq_len][hidden] where hidden = num_heads * head_dim
+    let mut out = vec![0.0f32; seq_len * hidden];
+    for s in 0..seq_len {
+        for h in 0..num_heads {
+            let src_off = (h * seq_len + s) * head_dim;
+            let dst_off = s * hidden + h * head_dim;
+            out[dst_off..dst_off + head_dim].copy_from_slice(&src[src_off..src_off + head_dim]);
+        }
+    }
+    Tensor::from_slice(&out, &[seq_len, hidden]).to_device(x.device())
+}
+
+/// Greedy sampling: return the argmax token ID from the last position's logits.
+pub fn sample_greedy(logits: &Tensor) -> u32 {
+    assert_eq!(logits.ndim(), 2); // [S, V]
+    let logits_cpu = logits.to_device(Device::Cpu);
+    let data = logits_cpu.as_slice::<f32>();
+    let vocab_size = logits.shape()[1];
+    let seq_len = logits.shape()[0];
+    let last_row = &data[(seq_len - 1) * vocab_size..seq_len * vocab_size];
+    last_row.iter()
+        .enumerate()
+        .max_by(|a, b| a.1.partial_cmp(b.1).unwrap())
+        .map(|(idx, _)| idx as u32)
+        .unwrap()
+}
--- a/crates/xserv-model/src/lib.rs
+++ b/crates/xserv-model/src/lib.rs
@@ -0,0 +1,6 @@
+pub mod config;
+pub mod gpt2;
+pub mod loader;
+
+pub use config::ModelConfig;
+pub use gpt2::GPT2;
--- a/crates/xserv-model/src/loader.rs
+++ b/crates/xserv-model/src/loader.rs
@@ -0,0 +1,87 @@
+use half::{bf16, f16};
+use safetensors::SafeTensors;
+use std::collections::HashMap;
+use std::path::Path;
+use xserv_tensor::{DType, Device, Tensor};
+
+pub fn load_safetensors(path: &Path, device: Device) -> HashMap<String, Tensor> {
+    let data = std::fs::read(path)
+        .unwrap_or_else(|e| panic!("failed to read {}: {e}", path.display()));
+    let st = SafeTensors::deserialize(&data)
+        .unwrap_or_else(|e| panic!("failed to parse safetensors {}: {e}", path.display()));
+
+    let mut tensors = HashMap::new();
+
+    for (name, view) in st.tensors() {
+        let shape: Vec<usize> = view.shape().to_vec();
+        let raw_bytes = view.data();
+        let dtype = match view.dtype() {
+            safetensors::Dtype::F32 => DType::F32,
+            safetensors::Dtype::F16 => DType::F16,
+            safetensors::Dtype::BF16 => DType::BF16,
+            other => {
+                eprintln!("skipping tensor {name}: unsupported dtype {other:?}");
+                continue;
+            }
+        };
+
+        let tensor = make_tensor(raw_bytes, &shape, dtype);
+        let tensor = tensor.to_device(device);
+        tensors.insert(name.to_string(), tensor);
+    }
+
+    tensors
+}
+
+/// Load from a directory containing model.safetensors (or sharded files) + config.json.
+pub fn load_model_dir(dir: &Path, device: Device) -> HashMap<String, Tensor> {
+    let single = dir.join("model.safetensors");
+    if single.exists() {
+        return load_safetensors(&single, device);
+    }
+
+    // Try sharded: model-00001-of-NNNNN.safetensors
+    let mut all_tensors = HashMap::new();
+    let mut entries: Vec<_> = std::fs::read_dir(dir)
+        .unwrap()
+        .filter_map(|e| e.ok())
+        .filter(|e| {
+            e.path()
+                .file_name()
+                .map(|f| f.to_string_lossy().ends_with(".safetensors"))
+                .unwrap_or(false)
+        })
+        .collect();
+    entries.sort_by_key(|e| e.file_name());
+
+    for entry in entries {
+        let tensors = load_safetensors(&entry.path(), device);
+        all_tensors.extend(tensors);
+    }
+
+    assert!(!all_tensors.is_empty(), "no safetensors files found in {}", dir.display());
+    all_tensors
+}
+
+fn make_tensor(raw_bytes: &[u8], shape: &[usize], dtype: DType) -> Tensor {
+    match dtype {
+        DType::F32 => {
+            let floats: &[f32] = unsafe {
+                std::slice::from_raw_parts(raw_bytes.as_ptr() as *const f32, raw_bytes.len() / 4)
+            };
+            Tensor::from_slice(floats, shape)
+        }
+        DType::F16 => {
+            let halfs: &[f16] = unsafe {
+                std::slice::from_raw_parts(raw_bytes.as_ptr() as *const f16, raw_bytes.len() / 2)
+            };
+            Tensor::from_slice(halfs, shape)
+        }
+        DType::BF16 => {
+            let bfs: &[bf16] = unsafe {
+                std::slice::from_raw_parts(raw_bytes.as_ptr() as *const bf16, raw_bytes.len() / 2)
+            };
+            Tensor::from_slice(bfs, shape)
+        }
+    }
+}
--- a/crates/xserv-tensor/src/tensor.rs
+++ b/crates/xserv-tensor/src/tensor.rs
@@ -137,8 +137,13 @@ impl Tensor {
        if self.is_contiguous() {
            return self.clone();
        }
-        // Copy to contiguous layout on CPU
-        assert_eq!(self.device(), Device::Cpu, "contiguous() on GPU not yet supported");
+        // For GPU tensors: round-trip through CPU (correct but slow).
+        // TODO: write a GPU contiguous-copy kernel for performance.
+        if matches!(self.device(), Device::Cuda(_)) {
+            let cpu = self.to_device(Device::Cpu);
+            let contig = cpu.contiguous();
+            return contig.to_device(self.device());
+        }
        let numel = self.numel();
        let elem_size = self.dtype.size_bytes();
        let src_bytes = self.storage.as_cpu_bytes();
@@ -173,17 +178,18 @@ impl Tensor {
    // --- Device transfer ---

    pub fn to_device(&self, device: Device) -> Self {
-        let t = if self.is_contiguous() { self.clone() } else { self.contiguous() };
-        if t.device() == device {
-            return t;
+        if self.device() == device {
+            return self.clone();
        }
-        let new_storage = t.storage.to_device(device).expect("device transfer failed");
+        // Transfer the raw storage (preserving strides/offset).
+        // Non-contiguous layout is preserved — the user can call contiguous() after.
+        let new_storage = self.storage.to_device(device).expect("device transfer failed");
        Self {
            storage: new_storage,
-            shape: t.shape,
-            strides: t.strides,
-            offset: 0,
-            dtype: t.dtype,
+            shape: self.shape.clone(),
+            strides: self.strides.clone(),
+            offset: self.offset,
+            dtype: self.dtype,
        }
    }

--- a/crates/xserv-tokenizer/Cargo.toml
+++ b/crates/xserv-tokenizer/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "xserv-tokenizer"
+version.workspace = true
+edition.workspace = true
+
+[dependencies]
+serde.workspace = true
+serde_json.workspace = true
+regex.workspace = true
--- a/crates/xserv-tokenizer/src/bpe.rs
+++ b/crates/xserv-tokenizer/src/bpe.rs
@@ -0,0 +1,251 @@
+use regex::Regex;
+use serde::Deserialize;
+use std::collections::HashMap;
+use std::path::Path;
+
+pub struct Tokenizer {
+    encoder: HashMap<Vec<u8>, u32>,
+    decoder: Vec<Vec<u8>>,
+    merge_ranks: HashMap<(u32, u32), usize>,
+    special_tokens: HashMap<String, u32>,
+    special_token_ids: HashMap<u32, String>,
+    pre_tokenize_re: Regex,
+    eos_token_id: Option<u32>,
+}
+
+#[derive(Deserialize)]
+struct TokenizerJson {
+    model: ModelSection,
+    #[serde(default)]
+    added_tokens: Vec<AddedToken>,
+}
+
+#[derive(Deserialize)]
+struct ModelSection {
+    vocab: HashMap<String, u32>,
+    merges: Vec<String>,
+}
+
+#[derive(Deserialize)]
+struct AddedToken {
+    id: u32,
+    content: String,
+    special: bool,
+}
+
+impl Tokenizer {
+    pub fn from_file(path: &Path) -> Self {
+        let data = std::fs::read_to_string(path)
+            .unwrap_or_else(|e| panic!("failed to read {}: {e}", path.display()));
+        let tj: TokenizerJson = serde_json::from_str(&data)
+            .unwrap_or_else(|e| panic!("failed to parse tokenizer.json: {e}"));
+
+        // Build encoder: token bytes → ID
+        let mut encoder = HashMap::new();
+        for (token_str, &id) in &tj.model.vocab {
+            let bytes = token_str_to_bytes(token_str);
+            encoder.insert(bytes, id);
+        }
+
+        // Build decoder: ID → token bytes
+        let max_id = tj.model.vocab.values().copied().max().unwrap_or(0);
+        let added_max = tj.added_tokens.iter().map(|t| t.id).max().unwrap_or(0);
+        let vocab_size = (max_id.max(added_max) + 1) as usize;
+        let mut decoder = vec![vec![]; vocab_size];
+        for (token_str, &id) in &tj.model.vocab {
+            decoder[id as usize] = token_str_to_bytes(token_str);
+        }
+
+        // Parse merges
+        let mut merge_ranks = HashMap::new();
+        for (rank, merge_line) in tj.model.merges.iter().enumerate() {
+            let parts: Vec<&str> = merge_line.splitn(2, ' ').collect();
+            if parts.len() != 2 { continue; }
+            let a_bytes = token_str_to_bytes(parts[0]);
+            let b_bytes = token_str_to_bytes(parts[1]);
+            if let (Some(&a_id), Some(&b_id)) = (encoder.get(&a_bytes), encoder.get(&b_bytes)) {
+                merge_ranks.insert((a_id, b_id), rank);
+            }
+        }
+
+        // Special tokens
+        let mut special_tokens = HashMap::new();
+        let mut special_token_ids = HashMap::new();
+        let mut eos_token_id = None;
+        for at in &tj.added_tokens {
+            if at.special {
+                special_tokens.insert(at.content.clone(), at.id);
+                special_token_ids.insert(at.id, at.content.clone());
+                decoder.resize(decoder.len().max(at.id as usize + 1), vec![]);
+                decoder[at.id as usize] = at.content.as_bytes().to_vec();
+                if at.content == "<|endoftext|>" || at.content == "<|end_of_text|>" {
+                    eos_token_id = Some(at.id);
+                }
+            }
+        }
+
+        // GPT-2 pre-tokenization regex.
+        // The original uses (?!\S) lookahead which Rust regex doesn't support.
+        // Simplified: collapse trailing whitespace into one match. Functionally equivalent
+        // for BPE since each whitespace chunk gets encoded independently anyway.
+        let pre_tokenize_re = Regex::new(
+            r"'s|'t|'re|'ve|'m|'ll|'d| ?\p{L}+| ?\p{N}+| ?[^\s\p{L}\p{N}]+|\s+"
+        ).unwrap();
+
+        Self {
+            encoder,
+            decoder,
+            merge_ranks,
+            special_tokens,
+            special_token_ids,
+            pre_tokenize_re,
+            eos_token_id,
+        }
+    }
+
+    pub fn encode(&self, text: &str) -> Vec<u32> {
+        let mut tokens = Vec::new();
+
+        // Check for special tokens first (split around them)
+        let mut remaining = text;
+        while !remaining.is_empty() {
+            // Find earliest special token
+            let mut earliest: Option<(usize, &str, u32)> = None;
+            for (st, &id) in &self.special_tokens {
+                if let Some(pos) = remaining.find(st.as_str()) {
+                    if earliest.is_none() || pos < earliest.unwrap().0 {
+                        earliest = Some((pos, st, id));
+                    }
+                }
+            }
+
+            if let Some((pos, st, id)) = earliest {
+                if pos > 0 {
+                    self.encode_ordinary(&remaining[..pos], &mut tokens);
+                }
+                tokens.push(id);
+                remaining = &remaining[pos + st.len()..];
+            } else {
+                self.encode_ordinary(remaining, &mut tokens);
+                break;
+            }
+        }
+
+        tokens
+    }
+
+    fn encode_ordinary(&self, text: &str, out: &mut Vec<u32>) {
+        for mat in self.pre_tokenize_re.find_iter(text) {
+            let word = mat.as_str();
+            let word_bytes: Vec<u8> = word.bytes().collect();
+            let mut token_ids: Vec<u32> = word_bytes.iter().map(|&b| {
+                *self.encoder.get(&vec![b]).unwrap_or_else(|| {
+                    panic!("byte {b} not in vocab")
+                })
+            }).collect();
+
+            // BPE merges
+            loop {
+                if token_ids.len() < 2 { break; }
+                let mut best_rank = usize::MAX;
+                let mut best_idx = 0;
+                for i in 0..token_ids.len() - 1 {
+                    if let Some(&rank) = self.merge_ranks.get(&(token_ids[i], token_ids[i + 1])) {
+                        if rank < best_rank {
+                            best_rank = rank;
+                            best_idx = i;
+                        }
+                    }
+                }
+                if best_rank == usize::MAX { break; }
+
+                let merged_bytes = [
+                    self.decoder[token_ids[best_idx] as usize].as_slice(),
+                    self.decoder[token_ids[best_idx + 1] as usize].as_slice(),
+                ].concat();
+                let merged_id = *self.encoder.get(&merged_bytes).unwrap_or_else(|| {
+                    panic!("merged token not in vocab");
+                });
+                token_ids[best_idx] = merged_id;
+                token_ids.remove(best_idx + 1);
+            }
+
+            out.extend_from_slice(&token_ids);
+        }
+    }
+
+    pub fn decode(&self, token_ids: &[u32]) -> String {
+        let mut bytes = Vec::new();
+        for &id in token_ids {
+            if let Some(b) = self.decoder.get(id as usize) {
+                bytes.extend_from_slice(b);
+            }
+        }
+        String::from_utf8_lossy(&bytes).into_owned()
+    }
+
+    pub fn eos_token_id(&self) -> Option<u32> {
+        self.eos_token_id
+    }
+
+    pub fn vocab_size(&self) -> usize {
+        self.decoder.len()
+    }
+
+    pub fn special_token_id(&self, name: &str) -> Option<u32> {
+        self.special_tokens.get(name).copied()
+    }
+}
+
+/// Convert a token string from HF vocab (which uses Unicode replacements for bytes)
+/// back to raw bytes. GPT-2 uses a byte-to-unicode mapping where e.g. byte 0x20 (space)
+/// is represented as 'Ġ' (U+0120).
+fn token_str_to_bytes(s: &str) -> Vec<u8> {
+    s.chars().map(|c| unicode_to_byte(c)).collect()
+}
+
+fn unicode_to_byte(c: char) -> u8 {
+    let u = c as u32;
+    // GPT-2 byte encoder: maps bytes 0-255 to specific Unicode code points.
+    // Printable ASCII bytes map to themselves. Others are shifted to 256+.
+    match u {
+        0x21..=0x7E => u as u8,        // '!' to '~'
+        0xA1..=0xAC => u as u8,        // '¡' to '¬'
+        0xAE..=0xFF => u as u8,        // '®' to 'ÿ'
+        // Shifted bytes: 0x100 + original_byte for bytes not in the above ranges
+        0x100..=0x1FF => (u - 0x100) as u8 + {
+            // The shift mapping: byte values 0..=32, 127..=160, 173
+            // are shifted to 256..=288, 289+, etc.
+            0
+        },
+        _ => {
+            // Fallback: for the GPT-2 byte encoder, specific mappings
+            byte_from_unicode_gpt2(c)
+        }
+    }
+}
+
+fn byte_from_unicode_gpt2(c: char) -> u8 {
+    // Build the inverse of GPT-2's bytes_to_unicode mapping.
+    // The mapping assigns printable chars to themselves and shifts unprintable bytes.
+    let u = c as u32;
+    // Direct ASCII printable + Latin-1 supplement printable ranges map identity
+    if (0x21..=0x7E).contains(&u) { return u as u8; }
+    if (0xA1..=0xAC).contains(&u) { return u as u8; }
+    if (0xAE..=0xFF).contains(&u) { return u as u8; }
+
+    // Shifted range: the remaining 68 bytes (0-32, 127-160, 173) get mapped to 256..=323
+    static SHIFTED_BYTES: &[u8] = &[
+        0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
+        24, 25, 26, 27, 28, 29, 30, 31, 32, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136,
+        137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153,
+        154, 155, 156, 157, 158, 159, 160, 173,
+    ];
+    let shifted_start = 256u32;
+    if u >= shifted_start && u < shifted_start + SHIFTED_BYTES.len() as u32 {
+        return SHIFTED_BYTES[(u - shifted_start) as usize];
+    }
+
+    // Shouldn't reach here for valid GPT-2 tokenizer
+    c as u8
+}
--- a/crates/xserv-tokenizer/src/lib.rs
+++ b/crates/xserv-tokenizer/src/lib.rs
@@ -0,0 +1,3 @@
+pub mod bpe;
+
+pub use bpe::Tokenizer;
--- a/csrc/activation/activations.cu
+++ b/csrc/activation/activations.cu
@@ -0,0 +1,90 @@
+#include <cuda_bf16.h>
+#include <math.h>
+
+// GELU (tanh approximation):
+// gelu(x) = 0.5 * x * (1 + tanh(sqrt(2/pi) * (x + 0.044715 * x^3)))
+__device__ __forceinline__ float gelu_f(float x) {
+    const float SQRT_2_OVER_PI = 0.7978845608f;
+    float cube = x * x * x;
+    float inner = SQRT_2_OVER_PI * (x + 0.044715f * cube);
+    return 0.5f * x * (1.0f + tanhf(inner));
+}
+
+// SiLU (Swish): silu(x) = x * sigmoid(x) = x / (1 + exp(-x))
+__device__ __forceinline__ float silu_f(float x) {
+    return x / (1.0f + expf(-x));
+}
+
+__global__ void gelu_f32(const float* x, float* out, int n) {
+    int idx = blockIdx.x * blockDim.x + threadIdx.x;
+    if (idx < n) out[idx] = gelu_f(x[idx]);
+}
+
+__global__ void gelu_bf16(const __nv_bfloat16* x, __nv_bfloat16* out, int n) {
+    int idx = blockIdx.x * blockDim.x + threadIdx.x;
+    if (idx < n) out[idx] = __float2bfloat16(gelu_f(__bfloat162float(x[idx])));
+}
+
+__global__ void silu_f32(const float* x, float* out, int n) {
+    int idx = blockIdx.x * blockDim.x + threadIdx.x;
+    if (idx < n) out[idx] = silu_f(x[idx]);
+}
+
+__global__ void silu_bf16(const __nv_bfloat16* x, __nv_bfloat16* out, int n) {
+    int idx = blockIdx.x * blockDim.x + threadIdx.x;
+    if (idx < n) out[idx] = __float2bfloat16(silu_f(__bfloat162float(x[idx])));
+}
+
+__global__ void scale_f32_kernel(const float* x, float* out, float scale, int n) {
+    int idx = blockIdx.x * blockDim.x + threadIdx.x;
+    if (idx < n) out[idx] = x[idx] * scale;
+}
+
+__global__ void scale_bf16_kernel(const __nv_bfloat16* x, __nv_bfloat16* out, float scale, int n) {
+    int idx = blockIdx.x * blockDim.x + threadIdx.x;
+    if (idx < n) out[idx] = __float2bfloat16(__bfloat162float(x[idx]) * scale);
+}
+
+extern "C" {
+
+void launch_gelu_f32(const void* x, void* out, int n, void* stream) {
+    int block = 256;
+    int grid = (n + block - 1) / block;
+    gelu_f32<<<grid, block, 0, (cudaStream_t)stream>>>((const float*)x, (float*)out, n);
+}
+
+void launch_gelu_bf16(const void* x, void* out, int n, void* stream) {
+    int block = 256;
+    int grid = (n + block - 1) / block;
+    gelu_bf16<<<grid, block, 0, (cudaStream_t)stream>>>(
+        (const __nv_bfloat16*)x, (__nv_bfloat16*)out, n);
+}
+
+void launch_silu_f32(const void* x, void* out, int n, void* stream) {
+    int block = 256;
+    int grid = (n + block - 1) / block;
+    silu_f32<<<grid, block, 0, (cudaStream_t)stream>>>((const float*)x, (float*)out, n);
+}
+
+void launch_silu_bf16(const void* x, void* out, int n, void* stream) {
+    int block = 256;
+    int grid = (n + block - 1) / block;
+    silu_bf16<<<grid, block, 0, (cudaStream_t)stream>>>(
+        (const __nv_bfloat16*)x, (__nv_bfloat16*)out, n);
+}
+
+void launch_scale_f32(const void* x, void* out, float scale, int n, void* stream) {
+    int block = 256;
+    int grid = (n + block - 1) / block;
+    scale_f32_kernel<<<grid, block, 0, (cudaStream_t)stream>>>(
+        (const float*)x, (float*)out, scale, n);
+}
+
+void launch_scale_bf16(const void* x, void* out, float scale, int n, void* stream) {
+    int block = 256;
+    int grid = (n + block - 1) / block;
+    scale_bf16_kernel<<<grid, block, 0, (cudaStream_t)stream>>>(
+        (const __nv_bfloat16*)x, (__nv_bfloat16*)out, scale, n);
+}
+
+}
--- a/csrc/attention/causal_mask.cu
+++ b/csrc/attention/causal_mask.cu
@@ -0,0 +1,53 @@
+#include <cuda_bf16.h>
+
+// Apply causal mask: set scores[row][col] = -inf where col > row + offset.
+// offset is used for KV cache: when query starts at position `offset`,
+// we allow attending to positions [0, offset + row].
+// scores: [batch, rows, cols]  (flattened batch×heads)
+
+__global__ void causal_mask_f32(
+    float* __restrict__ scores,
+    int rows, int cols, int offset
+) {
+    int batch_idx = blockIdx.z;
+    int row = blockIdx.y;
+    int col = blockIdx.x * blockDim.x + threadIdx.x;
+
+    if (col < cols && col > row + offset) {
+        scores[batch_idx * rows * cols + row * cols + col] = -INFINITY;
+    }
+}
+
+__global__ void causal_mask_bf16(
+    __nv_bfloat16* __restrict__ scores,
+    int rows, int cols, int offset
+) {
+    int batch_idx = blockIdx.z;
+    int row = blockIdx.y;
+    int col = blockIdx.x * blockDim.x + threadIdx.x;
+
+    if (col < cols && col > row + offset) {
+        // BF16 doesn't have proper -inf literal, use a very large negative
+        scores[batch_idx * rows * cols + row * cols + col] = __float2bfloat16(-1e9f);
+    }
+}
+
+extern "C" {
+
+void launch_causal_mask_f32(void* scores, int batch, int rows, int cols,
+                            int offset, void* stream) {
+    int block = 256;
+    dim3 grid((cols + block - 1) / block, rows, batch);
+    causal_mask_f32<<<grid, block, 0, (cudaStream_t)stream>>>(
+        (float*)scores, rows, cols, offset);
+}
+
+void launch_causal_mask_bf16(void* scores, int batch, int rows, int cols,
+                             int offset, void* stream) {
+    int block = 256;
+    dim3 grid((cols + block - 1) / block, rows, batch);
+    causal_mask_bf16<<<grid, block, 0, (cudaStream_t)stream>>>(
+        (__nv_bfloat16*)scores, rows, cols, offset);
+}
+
+}
--- a/csrc/common.cuh
+++ b/csrc/common.cuh
@@ -0,0 +1,50 @@
+#pragma once
+#include <cuda_bf16.h>
+
+// --- Warp-level reductions (no shared memory needed) ---
+
+__device__ __forceinline__ float warp_reduce_sum(float val) {
+    #pragma unroll
+    for (int offset = 16; offset > 0; offset >>= 1)
+        val += __shfl_down_sync(0xffffffff, val, offset);
+    return val;
+}
+
+__device__ __forceinline__ float warp_reduce_max(float val) {
+    #pragma unroll
+    for (int offset = 16; offset > 0; offset >>= 1)
+        val = fmaxf(val, __shfl_down_sync(0xffffffff, val, offset));
+    return val;
+}
+
+// --- Block-level reductions ---
+
+__device__ __forceinline__ float block_reduce_sum(float val) {
+    __shared__ float shared[32];
+    int lane = threadIdx.x & 31;
+    int warp_id = threadIdx.x >> 5;
+    int num_warps = (blockDim.x + 31) >> 5;
+
+    val = warp_reduce_sum(val);
+    if (lane == 0) shared[warp_id] = val;
+    __syncthreads();
+
+    val = (threadIdx.x < num_warps) ? shared[threadIdx.x] : 0.0f;
+    if (warp_id == 0) val = warp_reduce_sum(val);
+    return val;
+}
+
+__device__ __forceinline__ float block_reduce_max(float val) {
+    __shared__ float shared[32];
+    int lane = threadIdx.x & 31;
+    int warp_id = threadIdx.x >> 5;
+    int num_warps = (blockDim.x + 31) >> 5;
+
+    val = warp_reduce_max(val);
+    if (lane == 0) shared[warp_id] = val;
+    __syncthreads();
+
+    val = (threadIdx.x < num_warps) ? shared[threadIdx.x] : -INFINITY;
+    if (warp_id == 0) val = warp_reduce_max(val);
+    return val;
+}
--- a/csrc/embedding/embedding.cu
+++ b/csrc/embedding/embedding.cu
@@ -0,0 +1,55 @@
+#include <cuda_bf16.h>
+
+// Embedding lookup: out[seq_idx] = table[token_ids[seq_idx]]
+// Grid: num_tokens, Block: handles hidden_size elements per token.
+
+__global__ void embedding_f32(
+    const float* __restrict__ table,    // [vocab_size, hidden_size]
+    const int* __restrict__ token_ids,  // [num_tokens]
+    float* __restrict__ out,            // [num_tokens, hidden_size]
+    int hidden_size
+) {
+    int token_idx = blockIdx.x;
+    int tid = token_ids[token_idx];
+    const float* row = table + tid * hidden_size;
+    float* dst = out + token_idx * hidden_size;
+
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        dst[i] = row[i];
+    }
+}
+
+__global__ void embedding_bf16(
+    const __nv_bfloat16* __restrict__ table,
+    const int* __restrict__ token_ids,
+    __nv_bfloat16* __restrict__ out,
+    int hidden_size
+) {
+    int token_idx = blockIdx.x;
+    int tid = token_ids[token_idx];
+    const __nv_bfloat16* row = table + tid * hidden_size;
+    __nv_bfloat16* dst = out + token_idx * hidden_size;
+
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        dst[i] = row[i];
+    }
+}
+
+extern "C" {
+
+void launch_embedding_f32(const void* table, const void* token_ids, void* out,
+                          int num_tokens, int hidden_size, void* stream) {
+    int block = (hidden_size < 256) ? hidden_size : 256;
+    embedding_f32<<<num_tokens, block, 0, (cudaStream_t)stream>>>(
+        (const float*)table, (const int*)token_ids, (float*)out, hidden_size);
+}
+
+void launch_embedding_bf16(const void* table, const void* token_ids, void* out,
+                           int num_tokens, int hidden_size, void* stream) {
+    int block = (hidden_size < 256) ? hidden_size : 256;
+    embedding_bf16<<<num_tokens, block, 0, (cudaStream_t)stream>>>(
+        (const __nv_bfloat16*)table, (const int*)token_ids,
+        (__nv_bfloat16*)out, hidden_size);
+}
+
+}
--- a/csrc/embedding/rope.cu
+++ b/csrc/embedding/rope.cu
@@ -0,0 +1,116 @@
+#include <cuda_bf16.h>
+#include <math.h>
+
+// RoPE: Rotary Position Embedding
+// For each pair (x[2i], x[2i+1]) at position `pos`:
+//   y[2i]   = x[2i] * cos - x[2i+1] * sin
+//   y[2i+1] = x[2i] * sin + x[2i+1] * cos
+// where cos/sin come from precomputed cos_cache/sin_cache.
+//
+// cos_cache[pos][i] = cos(pos * freq[i])
+// sin_cache[pos][i] = sin(pos * freq[i])
+// freq[i] = 1.0 / (theta ^ (2i / head_dim))
+
+// Apply RoPE in-place to Q or K tensor.
+// x shape: [num_tokens, num_heads, head_dim]
+// cos_cache, sin_cache shape: [max_seq_len, head_dim/2]
+// positions: [num_tokens] — the position index for each token
+
+__global__ void rope_f32(
+    float* __restrict__ x,                    // [num_tokens, num_heads, head_dim]
+    const float* __restrict__ cos_cache,      // [max_seq_len, half_dim]
+    const float* __restrict__ sin_cache,      // [max_seq_len, half_dim]
+    const int* __restrict__ positions,        // [num_tokens]
+    int num_heads, int head_dim
+) {
+    int token_idx = blockIdx.x;
+    int head_idx = blockIdx.y;
+    int half_dim = head_dim / 2;
+    int pair_idx = threadIdx.x;  // which pair (0..half_dim)
+
+    if (pair_idx >= half_dim) return;
+
+    int pos = positions[token_idx];
+    float cos_val = cos_cache[pos * half_dim + pair_idx];
+    float sin_val = sin_cache[pos * half_dim + pair_idx];
+
+    int base = (token_idx * num_heads + head_idx) * head_dim;
+    float x0 = x[base + 2 * pair_idx];
+    float x1 = x[base + 2 * pair_idx + 1];
+
+    x[base + 2 * pair_idx]     = x0 * cos_val - x1 * sin_val;
+    x[base + 2 * pair_idx + 1] = x0 * sin_val + x1 * cos_val;
+}
+
+__global__ void rope_bf16(
+    __nv_bfloat16* __restrict__ x,
+    const float* __restrict__ cos_cache,
+    const float* __restrict__ sin_cache,
+    const int* __restrict__ positions,
+    int num_heads, int head_dim
+) {
+    int token_idx = blockIdx.x;
+    int head_idx = blockIdx.y;
+    int half_dim = head_dim / 2;
+    int pair_idx = threadIdx.x;
+
+    if (pair_idx >= half_dim) return;
+
+    int pos = positions[token_idx];
+    float cos_val = cos_cache[pos * half_dim + pair_idx];
+    float sin_val = sin_cache[pos * half_dim + pair_idx];
+
+    int base = (token_idx * num_heads + head_idx) * head_dim;
+    float x0 = __bfloat162float(x[base + 2 * pair_idx]);
+    float x1 = __bfloat162float(x[base + 2 * pair_idx + 1]);
+
+    x[base + 2 * pair_idx]     = __float2bfloat16(x0 * cos_val - x1 * sin_val);
+    x[base + 2 * pair_idx + 1] = __float2bfloat16(x0 * sin_val + x1 * cos_val);
+}
+
+// Precompute cos/sin cache on GPU
+__global__ void compute_rope_cache(
+    float* __restrict__ cos_cache,  // [max_seq_len, half_dim]
+    float* __restrict__ sin_cache,
+    int max_seq_len, int half_dim, float theta
+) {
+    int pos = blockIdx.x;
+    int i = threadIdx.x;
+    if (i >= half_dim) return;
+
+    float freq = 1.0f / powf(theta, (float)(2 * i) / (float)(2 * half_dim));
+    float angle = (float)pos * freq;
+    cos_cache[pos * half_dim + i] = cosf(angle);
+    sin_cache[pos * half_dim + i] = sinf(angle);
+}
+
+extern "C" {
+
+void launch_rope_f32(void* x, const void* cos_cache, const void* sin_cache,
+                     const void* positions, int num_tokens, int num_heads,
+                     int head_dim, void* stream) {
+    dim3 grid(num_tokens, num_heads);
+    int block = head_dim / 2;
+    rope_f32<<<grid, block, 0, (cudaStream_t)stream>>>(
+        (float*)x, (const float*)cos_cache, (const float*)sin_cache,
+        (const int*)positions, num_heads, head_dim);
+}
+
+void launch_rope_bf16(void* x, const void* cos_cache, const void* sin_cache,
+                      const void* positions, int num_tokens, int num_heads,
+                      int head_dim, void* stream) {
+    dim3 grid(num_tokens, num_heads);
+    int block = head_dim / 2;
+    rope_bf16<<<grid, block, 0, (cudaStream_t)stream>>>(
+        (__nv_bfloat16*)x, (const float*)cos_cache, (const float*)sin_cache,
+        (const int*)positions, num_heads, head_dim);
+}
+
+void launch_compute_rope_cache(void* cos_cache, void* sin_cache,
+                               int max_seq_len, int half_dim, float theta,
+                               void* stream) {
+    compute_rope_cache<<<max_seq_len, half_dim, 0, (cudaStream_t)stream>>>(
+        (float*)cos_cache, (float*)sin_cache, max_seq_len, half_dim, theta);
+}
+
+}
--- a/csrc/normalization/layernorm.cu
+++ b/csrc/normalization/layernorm.cu
@@ -0,0 +1,102 @@
+#include "../common.cuh"
+
+// LayerNorm: y[i] = gamma[i] * (x[i] - mean) / sqrt(var + eps) + beta[i]
+// Each block processes one row of shape [hidden_size].
+
+__global__ void layernorm_f32(
+    const float* __restrict__ x,
+    const float* __restrict__ gamma,
+    const float* __restrict__ beta,
+    float* __restrict__ out,
+    int hidden_size, float eps
+) {
+    int row = blockIdx.x;
+    const float* x_row = x + row * hidden_size;
+    float* out_row = out + row * hidden_size;
+
+    // Welford online: compute mean and variance in one pass
+    float local_sum = 0.0f;
+    float local_sum_sq = 0.0f;
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        float v = x_row[i];
+        local_sum += v;
+        local_sum_sq += v * v;
+    }
+    local_sum = block_reduce_sum(local_sum);
+    local_sum_sq = block_reduce_sum(local_sum_sq);
+
+    __shared__ float s_mean, s_inv_std;
+    if (threadIdx.x == 0) {
+        float mean = local_sum / hidden_size;
+        float var = local_sum_sq / hidden_size - mean * mean;
+        s_mean = mean;
+        s_inv_std = rsqrtf(var + eps);
+    }
+    __syncthreads();
+
+    float mean = s_mean;
+    float inv_std = s_inv_std;
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        out_row[i] = gamma[i] * (x_row[i] - mean) * inv_std + beta[i];
+    }
+}
+
+__global__ void layernorm_bf16(
+    const __nv_bfloat16* __restrict__ x,
+    const __nv_bfloat16* __restrict__ gamma,
+    const __nv_bfloat16* __restrict__ beta,
+    __nv_bfloat16* __restrict__ out,
+    int hidden_size, float eps
+) {
+    int row = blockIdx.x;
+    const __nv_bfloat16* x_row = x + row * hidden_size;
+    __nv_bfloat16* out_row = out + row * hidden_size;
+
+    float local_sum = 0.0f;
+    float local_sum_sq = 0.0f;
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        float v = __bfloat162float(x_row[i]);
+        local_sum += v;
+        local_sum_sq += v * v;
+    }
+    local_sum = block_reduce_sum(local_sum);
+    local_sum_sq = block_reduce_sum(local_sum_sq);
+
+    __shared__ float s_mean, s_inv_std;
+    if (threadIdx.x == 0) {
+        float mean = local_sum / hidden_size;
+        float var = local_sum_sq / hidden_size - mean * mean;
+        s_mean = mean;
+        s_inv_std = rsqrtf(var + eps);
+    }
+    __syncthreads();
+
+    float mean = s_mean;
+    float inv_std = s_inv_std;
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        float v = __bfloat162float(x_row[i]);
+        float g = __bfloat162float(gamma[i]);
+        float b = __bfloat162float(beta[i]);
+        out_row[i] = __float2bfloat16(g * (v - mean) * inv_std + b);
+    }
+}
+
+extern "C" {
+
+void launch_layernorm_f32(const void* x, const void* gamma, const void* beta,
+                          void* out, int rows, int hidden_size, float eps, void* stream) {
+    int block = (hidden_size < 1024) ? hidden_size : 1024;
+    layernorm_f32<<<rows, block, 0, (cudaStream_t)stream>>>(
+        (const float*)x, (const float*)gamma, (const float*)beta,
+        (float*)out, hidden_size, eps);
+}
+
+void launch_layernorm_bf16(const void* x, const void* gamma, const void* beta,
+                           void* out, int rows, int hidden_size, float eps, void* stream) {
+    int block = (hidden_size < 1024) ? hidden_size : 1024;
+    layernorm_bf16<<<rows, block, 0, (cudaStream_t)stream>>>(
+        (const __nv_bfloat16*)x, (const __nv_bfloat16*)gamma, (const __nv_bfloat16*)beta,
+        (__nv_bfloat16*)out, hidden_size, eps);
+}
+
+}
--- a/csrc/normalization/rmsnorm.cu
+++ b/csrc/normalization/rmsnorm.cu
@@ -0,0 +1,83 @@
+#include "../common.cuh"
+
+// RMSNorm: y[i] = x[i] * rsqrt(mean(x²) + eps) * gamma[i]
+// Each block processes one row of shape [hidden_size].
+
+__global__ void rmsnorm_f32(
+    const float* __restrict__ x,
+    const float* __restrict__ gamma,
+    float* __restrict__ out,
+    int hidden_size, float eps
+) {
+    int row = blockIdx.x;
+    const float* x_row = x + row * hidden_size;
+    float* out_row = out + row * hidden_size;
+
+    float sum_sq = 0.0f;
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        float v = x_row[i];
+        sum_sq += v * v;
+    }
+    sum_sq = block_reduce_sum(sum_sq);
+
+    __shared__ float s_rms_inv;
+    if (threadIdx.x == 0) {
+        s_rms_inv = rsqrtf(sum_sq / hidden_size + eps);
+    }
+    __syncthreads();
+
+    float rms_inv = s_rms_inv;
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        out_row[i] = x_row[i] * rms_inv * gamma[i];
+    }
+}
+
+__global__ void rmsnorm_bf16(
+    const __nv_bfloat16* __restrict__ x,
+    const __nv_bfloat16* __restrict__ gamma,
+    __nv_bfloat16* __restrict__ out,
+    int hidden_size, float eps
+) {
+    int row = blockIdx.x;
+    const __nv_bfloat16* x_row = x + row * hidden_size;
+    __nv_bfloat16* out_row = out + row * hidden_size;
+
+    float sum_sq = 0.0f;
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        float v = __bfloat162float(x_row[i]);
+        sum_sq += v * v;
+    }
+    sum_sq = block_reduce_sum(sum_sq);
+
+    __shared__ float s_rms_inv;
+    if (threadIdx.x == 0) {
+        s_rms_inv = rsqrtf(sum_sq / hidden_size + eps);
+    }
+    __syncthreads();
+
+    float rms_inv = s_rms_inv;
+    for (int i = threadIdx.x; i < hidden_size; i += blockDim.x) {
+        float v = __bfloat162float(x_row[i]);
+        float g = __bfloat162float(gamma[i]);
+        out_row[i] = __float2bfloat16(v * rms_inv * g);
+    }
+}
+
+extern "C" {
+
+void launch_rmsnorm_f32(const void* x, const void* gamma, void* out,
+                        int rows, int hidden_size, float eps, void* stream) {
+    int block = (hidden_size < 1024) ? hidden_size : 1024;
+    rmsnorm_f32<<<rows, block, 0, (cudaStream_t)stream>>>(
+        (const float*)x, (const float*)gamma, (float*)out, hidden_size, eps);
+}
+
+void launch_rmsnorm_bf16(const void* x, const void* gamma, void* out,
+                         int rows, int hidden_size, float eps, void* stream) {
+    int block = (hidden_size < 1024) ? hidden_size : 1024;
+    rmsnorm_bf16<<<rows, block, 0, (cudaStream_t)stream>>>(
+        (const __nv_bfloat16*)x, (const __nv_bfloat16*)gamma,
+        (__nv_bfloat16*)out, hidden_size, eps);
+}
+
+}
--- a/csrc/reduce/softmax.cu
+++ b/csrc/reduce/softmax.cu
@@ -0,0 +1,106 @@
+#include "../common.cuh"
+
+// Safe softmax along the last dimension.
+// Each block handles one row of length `cols`.
+// Three-pass: 1) find max, 2) exp + sum, 3) normalize.
+
+__global__ void softmax_f32(
+    const float* __restrict__ x,
+    float* __restrict__ out,
+    int cols
+) {
+    int row = blockIdx.x;
+    const float* x_row = x + row * cols;
+    float* out_row = out + row * cols;
+
+    // Pass 1: find max
+    float local_max = -INFINITY;
+    for (int i = threadIdx.x; i < cols; i += blockDim.x) {
+        local_max = fmaxf(local_max, x_row[i]);
+    }
+    float row_max = block_reduce_max(local_max);
+
+    __shared__ float s_max;
+    if (threadIdx.x == 0) s_max = row_max;
+    __syncthreads();
+    row_max = s_max;
+
+    // Pass 2: exp and sum
+    float local_sum = 0.0f;
+    for (int i = threadIdx.x; i < cols; i += blockDim.x) {
+        float e = expf(x_row[i] - row_max);
+        out_row[i] = e;
+        local_sum += e;
+    }
+    float row_sum = block_reduce_sum(local_sum);
+
+    __shared__ float s_inv_sum;
+    if (threadIdx.x == 0) s_inv_sum = 1.0f / row_sum;
+    __syncthreads();
+    float inv_sum = s_inv_sum;
+
+    // Pass 3: normalize
+    for (int i = threadIdx.x; i < cols; i += blockDim.x) {
+        out_row[i] *= inv_sum;
+    }
+}
+
+__global__ void softmax_bf16(
+    const __nv_bfloat16* __restrict__ x,
+    __nv_bfloat16* __restrict__ out,
+    int cols
+) {
+    int row = blockIdx.x;
+    const __nv_bfloat16* x_row = x + row * cols;
+    __nv_bfloat16* out_row = out + row * cols;
+
+    float local_max = -INFINITY;
+    for (int i = threadIdx.x; i < cols; i += blockDim.x) {
+        local_max = fmaxf(local_max, __bfloat162float(x_row[i]));
+    }
+    float row_max = block_reduce_max(local_max);
+
+    __shared__ float s_max;
+    if (threadIdx.x == 0) s_max = row_max;
+    __syncthreads();
+    row_max = s_max;
+
+    // We need float scratch for exp values. Reuse out (write bf16 in pass 3).
+    // Use registers to hold exp values during sum pass instead.
+    float local_sum = 0.0f;
+    for (int i = threadIdx.x; i < cols; i += blockDim.x) {
+        float e = expf(__bfloat162float(x_row[i]) - row_max);
+        // Temporarily store exp in output as bf16 (slight precision loss, acceptable)
+        out_row[i] = __float2bfloat16(e);
+        local_sum += e;
+    }
+    float row_sum = block_reduce_sum(local_sum);
+
+    __shared__ float s_inv_sum;
+    if (threadIdx.x == 0) s_inv_sum = 1.0f / row_sum;
+    __syncthreads();
+    float inv_sum = s_inv_sum;
+
+    for (int i = threadIdx.x; i < cols; i += blockDim.x) {
+        float e = __bfloat162float(out_row[i]);
+        out_row[i] = __float2bfloat16(e * inv_sum);
+    }
+}
+
+extern "C" {
+
+void launch_softmax_f32(const void* x, void* out, int rows, int cols, void* stream) {
+    int block = (cols < 1024) ? cols : 1024;
+    if (block < 32) block = 32;
+    softmax_f32<<<rows, block, 0, (cudaStream_t)stream>>>(
+        (const float*)x, (float*)out, cols);
+}
+
+void launch_softmax_bf16(const void* x, void* out, int rows, int cols, void* stream) {
+    int block = (cols < 1024) ? cols : 1024;
+    if (block < 32) block = 32;
+    softmax_bf16<<<rows, block, 0, (cudaStream_t)stream>>>(
+        (const __nv_bfloat16*)x, (__nv_bfloat16*)out, cols);
+}
+
+}
--- a/docs/01-cuda-ffi.md
+++ b/docs/01-cuda-ffi.md
@@ -72,9 +72,31 @@ Wraps cudaStream_t. RAII with Drop calling cudaStreamDestroy.
 - `build.rs` uses `cc` crate to compile .cu files, link CUDA runtime

 ## Test Plan
-1. Device info: print GPU name, memory, compute capability, SM count
-2. GpuBuffer: alloc 1GB, H2D copy, D2H copy, verify data
-3. Vector add kernel: launch from Rust, verify output
-4. CachingAllocator: alloc→free→realloc same size uses cache (no new cudaMalloc)
-5. Multi-stream: two concurrent memcpy on different streams
-6. Benchmark: caching allocator vs raw cudaMalloc (100 cycles)
+
+- [x] Device info: print GPU name, memory, compute capability, SM count
+- [x] GpuBuffer: alloc → H2D copy → D2H copy → verify data (256B, 64MB)
+- [x] GpuBuffer: D2D copy 验证
+- [x] GpuBuffer: zero fill 验证
+- [x] Vector add kernel: launch from Rust, verify output
+- [x] CachingAllocator: alloc→free→realloc same size uses cache (no new cudaMalloc)
+- [x] CachingAllocator: 不同 size bucket 独立缓存
+- [x] CudaStream: 创建、同步、Drop
+- [x] PinnedBuffer: page-locked host memory
+- [x] Async copy: H2D async + D2H async via stream
+
+## Takeaways
+
+1. **`cudaDeviceProp` struct 布局不可靠**：CUDA 版本之间 `cudaDeviceProp` 的字段偏移会变化。我们最初用 struct 映射读取 `total_global_mem`，得到了垃圾值（12TB）。正确做法：用 `cudaMemGetInfo` 获取显存信息，用 `cudaDeviceGetAttribute` 获取其他属性。只从 `cudaDeviceProp` 读取 `name` 字段（始终在 struct 最前面，布局稳定）。
+
+2. **Rust 2024 edition 的 unsafe 语义变更**：
+   - `extern "C"` 块必须加 `unsafe` 前缀 → `unsafe extern "C"`
+   - `unsafe fn` 内部的 unsafe 调用也需要显式 `unsafe {}` 块
+   - 这让代码更安全，但初次移植需要注意
+
+3. **`cc` crate 的 CUDA 支持是内置的**：不需要 `features = ["cuda"]`（这个 feature 不存在）。只需 `.cuda(true).cudart("shared")`。
+
+4. **Caching Allocator 的 bucket 策略**：round up to next power of 2（最小 512B）。这意味着申请 513B 会分配 1024B，存在内部碎片。但简单且高效——避免了 free list 中的精确匹配问题。PyTorch 的 CUDACachingAllocator 用了更复杂的策略（best-fit with splitting），但对于推理场景，power-of-2 bucket 已经够用。
+
+5. **`into_raw` + `from_raw` 模式**：GpuBuffer 的 RAII Drop 和 CachingAllocator 的缓存需求冲突——allocator 需要持有裸指针而不触发 Drop。`into_raw()` 消费 self（`mem::forget`），返回裸指针；`from_raw()` 重新封装。这是 Rust 中管理 RAII 生命周期的标准模式。
+
+6. **dash5 环境**：CUDA 12.9 已安装但 `nvcc` 不在 PATH（需要 `/usr/local/cuda/bin`）。Rust 需要手动安装 rustup。无 rsync，用 `tar | ssh tar` 同步代码。开发工作流：本地写码 → tar sync → 远程 build+test。
--- a/docs/02-tensor.md
+++ b/docs/02-tensor.md
@@ -0,0 +1,97 @@
+# Phase 2: Tensor Abstraction Layer — Design Document
+
+## Goal
+
+实现核心 Tensor 类型，支持 CPU/GPU 存储、多种数据类型、strided view 操作，作为后续所有算子和模型的数据基础。
+
+## Module Layout
+
+```
+crates/xserv-tensor/
+├── Cargo.toml
+└── src/
+    ├── lib.rs          # re-exports
+    ├── dtype.rs        # DType enum, TensorDType trait
+    ├── shape.rs        # strides 计算, broadcast 规则
+    ├── storage.rs      # Storage (Arc引用计数), Device enum
+    └── tensor.rs       # Tensor 主体: 创建, 形状操作, 设备迁移
+```
+
+## Key Design Decisions
+
+### DType + TensorDType Trait
+
+```rust
+pub enum DType { F32, F16, BF16 }
+
+pub trait TensorDType: Copy + Send + Sync + 'static {
+    const DTYPE: DType;
+    fn to_f64(self) -> f64;
+    fn from_f64(v: f64) -> Self;
+}
+```
+
+- 用 `half` crate 的 `bf16`/`f16` 表示半精度类型
+- `TensorDType` trait 让 `from_slice<T>` 和 `as_slice<T>` 有类型安全
+- GPU kernel 中通过 `DType` dispatch 到对应的 CUDA 类型 (`__nv_bfloat16` / `float`)
+
+### Storage 引用计数
+
+```rust
+pub struct Storage(Arc<StorageInner>);
+enum StorageInner {
+    Cpu { data: Vec<u8> },
+    Cuda { buffer: GpuBuffer },
+}
+```
+
+- `Arc` 引用计数让 transpose/slice/reshape 能共享底层数据（view 语义）
+- 不实现 CoW（copy-on-write），view 只能读不能写
+- `to_device()` 总是创建新的 Storage
+
+### Strided Tensor
+
+```rust
+pub struct Tensor {
+    storage: Storage,
+    shape: SmallVec<[usize; 4]>,
+    strides: SmallVec<[usize; 4]>,
+    offset: usize,
+    dtype: DType,
+}
+```
+
+- `SmallVec<[usize; 4]>` 避免大多数 tensor (≤4D) 的堆分配
+- `strides` 以元素为单位（不是字节）
+- `offset` 支持 slice 操作（view 到 storage 的中间位置）
+- `is_contiguous()` 检查 strides 是否与 shape 匹配
+- 非 contiguous 的 tensor 调 `contiguous()` 才能送入 CUDA kernel
+
+### Broadcast 规则
+
+实现了 NumPy-style broadcasting:
+- 维度从尾部对齐
+- 大小为 1 的维度可以广播到任意大小
+- `broadcast_strides()` 将 size=1 维度的 stride 置为 0（虚拟广播，不复制数据）
+
+## Test Plan
+
+- [x] from_slice → shape/strides 正确
+- [x] reshape, transpose, squeeze, unsqueeze
+- [x] transpose 后 contiguous() 重排数据
+- [x] BF16 tensor 的精度验证
+- [x] CPU↔GPU roundtrip
+- [x] zeros on GPU → 拷回 CPU 验证全 0
+- [x] broadcast_shape 单元测试
+
+## Takeaways
+
+1. **`SmallVec` 是正确选择**：绝大多数 tensor ≤ 4D，避免了频繁堆分配。LLM 推理中常见的维度是 `[B, S, H]` (3D) 和 `[B, H, S, D]` (4D)。
+
+2. **View 语义的取舍**：Arc 共享 storage 实现了零拷贝 transpose/reshape，但代价是无法原地修改 view 后的 tensor。对于推理引擎这是可以接受的——推理路径上大部分操作是只读的。
+
+3. **contiguous() 的隐性开销**：非 contiguous tensor 在送入 kernel 前需要 `contiguous()` 拷贝。这意味着 `transpose → matmul` 会产生一次额外拷贝。后续优化方向：在 kernel 中直接支持 strided input。
+
+4. **Rust 2024 edition 变化**：`unsafe fn` 内部的 unsafe 调用也需要显式 `unsafe {}` 块，`extern "C"` 块必须加 `unsafe` 前缀。这个 edition 对安全性更严格。
+
+5. **CPU 实现先行**：先在 CPU 上验证逻辑正确性（如 contiguous 重排），再扩展到 GPU。这个策略在后续 phase 中应该继续沿用。
--- a/docs/03-gemm.md
+++ b/docs/03-gemm.md
@@ -0,0 +1,102 @@
+# Phase 3: GEMM — Design Document
+
+## Goal
+
+实现矩阵乘法的多个版本（naive → tiled → cuBLAS），建立 benchmark 对比框架，深入理解 GPU 编程中的内存访问模式和优化手段。
+
+## Module Layout
+
+```
+csrc/gemm/
+├── naive.cu          # 每个 thread 算一个输出元素
+└── tiled.cu          # shared memory tiling, 32x32 tiles
+
+crates/xserv-kernels/
+├── build.rs          # 编译 .cu + 链接 cublas
+└── src/
+    ├── lib.rs
+    └── gemm.rs       # FFI 封装, GemmBackend enum, matmul(), CublasContext
+```
+
+## Kernel Implementations
+
+### Version 1: Naive GEMM
+
+```
+Grid:  (ceil(N/16), ceil(M/16))
+Block: (16, 16)
+每个 thread: C[row][col] = sum_k(A[row][k] * B[k][col])
+```
+
+- 每个 thread 独立遍历 K 维度做点积
+- 所有读取走 global memory，无局部性优化
+- BF16 版本在 FP32 中累加（`__bfloat162float` → 累加 → `__float2bfloat16`）
+
+### Version 2: Tiled GEMM (Shared Memory)
+
+```
+TILE_SIZE = 32
+Grid:  (ceil(N/32), ceil(M/32))
+Block: (32, 32) = 1024 threads
+
+每个 tile iteration:
+  1. 协作加载 A[tile] 和 B[tile] 到 shared memory
+  2. __syncthreads()
+  3. 在 shared memory 中做 32 次乘加
+  4. __syncthreads()
+```
+
+- 每个 global memory 读取被 TILE_SIZE 个 thread 复用
+- 理论上减少 global memory 访问 TILE_SIZE 倍
+- BF16 版本同样在 shared memory 中存 float（FP32 累加）
+
+### Version 3: cuBLAS
+
+- `cublasGemmEx` 支持混合精度
+- **Row-major 适配**：cuBLAS 使用 column-major 布局，我们的 tensor 是 row-major
+  - 利用恒等式：`C = A @ B` (row-major) ⟺ `C^T = B^T @ A^T` (col-major)
+  - 传入 `CUBLAS_OP_N`，让 cuBLAS 把我们的 row-major 数据当作 col-major 的转置
+  - 参数：`m=N, n=M, k=K, lda=N (B), ldb=K (A), ldc=N (C)`
+
+### Backend Registry
+
+```rust
+pub enum GemmBackend { Naive, Tiled, CuBlas }
+pub fn matmul(a: &Tensor, b: &Tensor, backend: GemmBackend) -> Tensor;
+```
+
+运行时可切换 backend，方便 benchmark 对比和逐步替换。
+
+## CublasContext
+
+RAII 封装 `cublasHandle_t`，Drop 时调 `cublasDestroy_v2`。
+目前每次 matmul 创建一个新 handle，后续优化为全局复用。
+
+## Test Plan
+
+- [x] F32: naive/tiled/cuBLAS × small(4)/medium(64-256)/rect(65x33x97) 
+- [x] BF16: naive/tiled/cuBLAS × small/medium
+- [x] 三种 backend 在相同输入上输出一致（cross-backend consistency）
+- [x] 非方阵测试（M≠N≠K）
+- [x] 1024x1024 cuBLAS 验证
+
+## Takeaways
+
+1. **Row-major vs Column-major 陷阱**：这是 GEMM 实现中最容易出错的地方。cuBLAS 的 column-major 假设与 C/Rust 的 row-major 冲突。理解 `C=AB` ⟺ `C^T=B^T A^T` 这个恒等式是关键。实际做法：不做任何显式转置，只是交换 A/B 的传入顺序和调整 leading dimension 参数。
+
+2. **BF16 的累加精度**：BF16 只有 ~3 位有效数字（vs FP32 的 ~7 位）。如果在 BF16 中累加 K 次乘法，误差会快速放大。正确做法是**在 FP32 中累加，最后才转回 BF16**。我们的 naive 和 tiled kernel 都遵循了这一点（`float sum = 0.0f`）。cuBLAS 通过 `CUBLAS_COMPUTE_32F` 参数控制。
+
+3. **Shared memory tiling 的核心思想**：global memory 带宽是 GPU 计算的主要瓶颈。通过 shared memory tiling，每个数据从 global memory 读一次，被 TILE_SIZE 个 thread 复用。对于 TILE_SIZE=32，理论上减少 32 倍 global memory 访问。
+
+4. **`__syncthreads()` 的位置关键**：tile 加载后必须同步（确保所有 thread 写完 shared memory），计算后也要同步（防止下一轮加载覆盖还在使用的数据）。漏掉任何一个 sync 都会产生 race condition 导致结果错误。
+
+5. **cuBLAS handle 开销**：每次 matmul 创建/销毁 handle 有~0.1ms 开销。生产环境应全局复用一个 handle。Phase 15（性能优化）时需要修复这个问题。
+
+6. **`error::check` 需要 pub**：Phase 1 中 `check()` 是 `pub(crate)`，Phase 3 需要跨 crate 调用。反思：基础设施 crate 的错误处理函数应该从一开始就设计为 public API。
+
+## 后续优化方向（Phase 15）
+
+- Register tiling（每个 thread 算多个输出元素）
+- Tensor Core WMMA（利用 5090 的硬件加速）
+- CublasContext 全局复用
+- 非 contiguous input 支持（避免 matmul 前的拷贝）
--- a/docs/04-transformer-kernels.md
+++ b/docs/04-transformer-kernels.md
@@ -0,0 +1,213 @@
+# Phase 4: Transformer Core Kernels — Design Document
+
+## Goal
+
+实现 Transformer 所需的所有非 Attention 算子的 CUDA kernel，每个 kernel 都支持 BF16 和 F32，与 PyTorch 参考实现对比验证。
+
+## Kernel 清单
+
+| Kernel | 用于 | 核心计算 | 关键优化点 |
+|--------|------|---------|-----------|
+| LayerNorm | GPT-2 | `(x - mean) / sqrt(var + eps) * gamma + beta` | Welford online, warp reduce |
+| RMSNorm | Qwen3 | `x / sqrt(mean(x²) + eps) * gamma` | 无 mean，比 LayerNorm 简单 |
+| GELU | GPT-2 | `0.5x(1 + tanh(sqrt(2/π)(x + 0.044715x³)))` | tanh 近似，逐元素 |
+| SiLU | Qwen3 | `x * sigmoid(x)` | 逐元素 |
+| Softmax | Attention | `exp(x - max) / sum(exp(x - max))` | Online safe softmax, warp reduce |
+| Embedding | 全部 | `output[i] = table[token_ids[i]]` | Gather, coalesced write |
+| RoPE | Qwen3 | 对 Q/K 的相邻元素对做旋转 | Precompute freq, in-place |
+
+## 文件布局
+
+```
+csrc/
+├── normalization/
+│   ├── layernorm.cu
+│   └── rmsnorm.cu
+├── activation/
+│   ├── gelu.cu
+│   └── silu.cu
+├── reduce/
+│   └── softmax.cu
+├── embedding/
+│   ├── embedding.cu
+│   └── rope.cu
+
+crates/xserv-kernels/src/
+├── layernorm.rs
+├── rmsnorm.rs
+├── activation.rs      # GELU + SiLU
+├── softmax.rs
+├── embedding.rs
+├── rope.rs
+└── lib.rs             # 新增 mod 声明
+```
+
+## Kernel 设计细节
+
+### LayerNorm
+
+输入 `x: [*, hidden_size]`, 输出 `y: [*, hidden_size]`
+参数 `gamma, beta: [hidden_size]`
+
+```
+y[i] = gamma[i] * (x[i] - mean) / sqrt(var + eps) + beta[i]
+```
+
+**GPU 映射**: 每个 thread block 处理一行（一个 hidden_size 向量）。
+- Phase 1: 并行加载 x，Welford online 算法计算 mean 和 var
+- Phase 2: warp-level reduce (`__shfl_down_sync`) 聚合 mean/var
+- Phase 3: block-level reduce via shared memory
+- Phase 4: 每个 thread 对自己负责的元素做 normalize + affine
+
+**Block 配置**: `block = min(1024, hidden_size)`, `grid = num_rows`
+
+### RMSNorm
+
+比 LayerNorm 简单：不减 mean，只做 `x * rsqrt(mean(x²) + eps) * gamma`。
+
+```
+rms = sqrt(sum(x²) / hidden_size + eps)
+y[i] = x[i] / rms * gamma[i]
+```
+
+**GPU 映射**: 同 LayerNorm，每个 block 处理一行。
+- 只需要一次 reduce（求 sum(x²)），不需要两次（mean + var）。
+
+### GELU
+
+逐元素操作，用 tanh 近似:
+```
+gelu(x) = 0.5 * x * (1 + tanh(sqrt(2/π) * (x + 0.044715 * x³)))
+```
+
+**GPU 映射**: 每个 thread 处理多个元素（向量化），grid 覆盖全部元素。
+
+### SiLU (Swish)
+
+逐元素: `silu(x) = x * sigmoid(x) = x / (1 + exp(-x))`
+
+### Softmax
+
+输入 `x: [*, seq_len]`, 沿最后一维做 softmax:
+```
+1. m = max(x)                    // 数值稳定
+2. e[i] = exp(x[i] - m)
+3. s = sum(e)
+4. y[i] = e[i] / s
+```
+
+**GPU 映射**: 每个 block 处理一行。
+- 第一遍 reduce: 求 max
+- 第二遍: exp(x - max) 并 reduce sum
+- 第三遍: 除以 sum
+
+**优化**: 可以用 online softmax 合并前两遍（边算 exp 边更新 max），但先实现三遍版本保证正确。
+
+### Embedding
+
+```
+output[seq_idx] = embedding_table[token_ids[seq_idx]]
+```
+
+**GPU 映射**: 每个 thread 处理一个 token 的部分维度。
+- `grid = num_tokens`, `block = hidden_size`（或分多个 thread 处理一个 token）
+- 写端是 coalesced（连续 thread 写连续地址），读端是 gather（非连续）
+
+### RoPE (Rotary Position Embedding)
+
+对 Q/K 的每对相邻元素 `(x0, x1)` 做 2D 旋转:
+```
+freq[i] = 1.0 / (theta ^ (2i / dim))
+cos_val = cos(position * freq[i])
+sin_val = sin(position * freq[i])
+y0 = x0 * cos_val - x1 * sin_val
+y1 = x0 * sin_val + x1 * cos_val
+```
+
+**GPU 映射**: 每个 thread 处理一对元素 `(x[2i], x[2i+1])`。
+- Precompute `cos_cache[max_seq_len][head_dim/2]` 和 `sin_cache` 在初始化时
+- 运行时 kernel 只做乘加
+
+**theta**: Qwen3 默认 `rope_theta = 1000000.0`
+
+## Reduction Pattern（核心学习点）
+
+所有 Norm 和 Softmax 都涉及 reduction。GPU reduction 的分层结构:
+
+```
+Thread-level:  每个 thread 处理多个元素，本地累加
+    ↓
+Warp-level:    __shfl_down_sync() 在 32 threads 内规约（无需 shared memory）
+    ↓
+Block-level:   shared memory 存各 warp 的结果，warp 0 再规约
+```
+
+对于 hidden_size <= 8192（LLM 常见），一个 block 足够，不需要 grid-level reduction。
+
+### Warp Reduce 模板
+
+```cuda
+__device__ float warp_reduce_sum(float val) {
+    for (int offset = 16; offset > 0; offset >>= 1)
+        val += __shfl_down_sync(0xffffffff, val, offset);
+    return val;
+}
+```
+
+### Block Reduce 模板
+
+```cuda
+__device__ float block_reduce_sum(float val) {
+    __shared__ float shared[32];  // max 32 warps per block
+    int lane = threadIdx.x % 32;
+    int warp_id = threadIdx.x / 32;
+
+    val = warp_reduce_sum(val);
+    if (lane == 0) shared[warp_id] = val;
+    __syncthreads();
+
+    val = (threadIdx.x < blockDim.x / 32) ? shared[lane] : 0.0f;
+    if (warp_id == 0) val = warp_reduce_sum(val);
+    return val;
+}
+```
+
+## Reference 验证策略
+
+写 `tools/generate_reference.py` 脚本，用 PyTorch 为每个 op 生成 reference input/output:
+- 保存为 `.npy` 格式
+- Rust 测试中加载对比
+- 或者直接在 Rust 测试中用 CPU 实现计算 expected 值（更简单，不依赖 Python）
+
+**选择**: 先用 Rust CPU 实现作为 reference（简单），关键 op（RoPE）再与 PyTorch 对比。
+
+## Test Plan
+
+- [x] RMSNorm F32: hidden_size=768, 4 rows → max_err 7.2e-7
+- [x] RMSNorm BF16: 同上 → max_err 7.0e-3
+- [x] LayerNorm F32: hidden_size=768 → max_err 1.7e-6
+- [x] GELU F32: 10000 elements → max_err 3.0e-8
+- [x] GELU BF16: 同上 → max_err 2.4e-3
+- [x] SiLU F32: 10000 elements → max_err 1.5e-8
+- [x] Softmax F32: 8×256 → max_err 1.4e-9
+- [x] Softmax sum=1 验证: 4×2048
+- [x] Softmax 大值 (1000+) 数值稳定性 → max_err 1.5e-8
+- [x] Embedding F32: vocab=100, hidden=64, 5 tokens → exact match
+- [x] RoPE F32: 4 tokens × 2 heads × dim=8 → max_err 6.0e-8
+- [x] RoPE position=0 恒等验证 → max_err 0
+
+## Takeaways
+
+1. **`common.cuh` 抽取共用 reduction 是正确的做法**：`warp_reduce_sum/max` 和 `block_reduce_sum/max` 被 RMSNorm, LayerNorm, Softmax 三个 kernel 复用。抽到头文件避免了代码重复，也确保 reduction 逻辑一致。build.rs 中需要 `.include("../../csrc")` 让 nvcc 能找到头文件。
+
+2. **Shared memory 中广播标量的模式**：Norm 和 Softmax 都需要将 reduce 结果（mean, rms_inv, max, sum）广播给 block 内所有 thread。标准做法：thread 0 写 `__shared__` 变量，`__syncthreads()` 后所有 thread 读。这比让每个 thread 独立做 reduce 高效得多。
+
+3. **Softmax 三遍 vs 两遍**：我们实现了三遍版本（max → exp+sum → normalize），简单可靠。Online softmax 可以合并前两遍（一遍 pass 内同时跟踪 running max 和 running sum），但需要更复杂的数值更新公式。Flash Attention（Phase 14）会用到 online softmax。
+
+4. **RoPE 的 position=0 恒等性**：`cos(0)=1, sin(0)=0`，所以 position 0 的旋转是恒等变换。这是一个很好的 sanity check。如果 position=0 时输出不等于输入，说明 kernel 有 bug。
+
+5. **BF16 Softmax 的精度陷阱**：exp 结果先写成 BF16 再读回做 normalize 会丢精度。理想做法是用 float scratch buffer 暂存 exp 结果。当前实现可接受（误差在 1e-2 量级），但在 attention score 很接近时可能引入可观察的差异。Phase 14 Flash Attention 会解决这个问题（全程 FP32 累加）。
+
+6. **Embedding 就是 gather 操作**：没有任何计算，纯粹的内存搬运。瓶颈在 global memory 随机读取（token_ids 导致不连续读 table）。写端是 coalesced 的（连续 token 写连续地址）。优化方向：使用向量化加载（`float4`）一次读 128 bit。
+
+7. **RoPE in-place 修改 Tensor 的设计考量**：RoPE 在数学上是对 Q/K 的 in-place 旋转。我们通过 `data_ptr() as *mut` 绕过了 Rust 的不可变借用。这在 GPU 上是安全的（kernel 内部互不干扰），但 Rust 侧没有 `&mut` 语义保护。后续如果需要更严格的安全性，可以引入 `Tensor::as_mut_ptr()` 方法并要求 `&mut self`。
--- a/docs/05-attention.md
+++ b/docs/05-attention.md
@@ -0,0 +1,92 @@
+# Phase 5: Naive Attention Kernel — Design Document
+
+## Goal
+
+实现标准 Multi-Head Attention（不做 Flash/Paged 优化），用组合式方法（GEMM + Softmax）完成。这是理解 attention 计算流程的基础，也是后续 Flash Attention 的 baseline。
+
+## 计算流程
+
+```
+Input: Q [B, H, S, D], K [B, H, S, D], V [B, H, S, D]
+       B=batch, H=num_heads, S=seq_len, D=head_dim
+
+1. scores = Q @ K^T / sqrt(D)           → [B, H, S, S]
+2. scores += causal_mask                 → 上三角置为 -inf
+3. weights = softmax(scores, dim=-1)     → [B, H, S, S]
+4. output = weights @ V                  → [B, H, S, D]
+```
+
+## 设计选择
+
+### 组合式实现（Phase 3 GEMM + Phase 4 Softmax）
+
+不写新的 fused CUDA kernel，而是复用已有的 matmul 和 softmax：
+- `scores = batched_matmul(Q, K^T)` — 需要支持 batched GEMM
+- `masked_fill(scores, causal_mask, -inf)` — 新的逐元素 kernel
+- `softmax(scores)` — 复用 Phase 4
+- `output = batched_matmul(weights, V)` — 复用 batched GEMM
+
+这意味着需要先扩展 matmul 支持 batched GEMM（cublasGemmStridedBatchedEx）。
+
+### Causal Mask
+
+不显式构造 mask 矩阵。写一个 kernel：
+```
+if (col > row + offset) score = -infinity
+```
+其中 offset 用于支持 KV cache 场景（decode 时 query 的 row 偏移）。
+
+### Batched GEMM via cuBLAS
+
+`cublasGemmStridedBatchedEx` 在一个 batch 维度上并行执行多个 GEMM：
+```
+C[b] = A[b] @ B[b]  for b = 0..batch_count
+stride_a = M * K, stride_b = K * N, stride_c = M * N
+```
+
+Attention 中 batch 维度 = B * H（batch_size × num_heads）。
+
+## 文件布局
+
+```
+csrc/attention/
+└── causal_mask.cu      # causal mask fill kernel
+
+crates/xserv-kernels/src/
+├── gemm.rs             # 扩展: batched_matmul
+├── attention.rs        # NEW: multi_head_attention()
+└── causal_mask.rs      # NEW: causal mask apply
+```
+
+## API 设计
+
+```rust
+/// Multi-head attention (naive, materializes S×S scores).
+/// q, k, v: [batch, num_heads, seq_len, head_dim]
+/// Returns: [batch, num_heads, seq_len, head_dim]
+pub fn attention(q: &Tensor, k: &Tensor, v: &Tensor, causal: bool) -> Tensor;
+
+/// Batched matmul: A[b] @ B[b] for all b.
+/// a: [..., M, K], b: [..., K, N] → [..., M, N]
+pub fn batched_matmul(a: &Tensor, b: &Tensor) -> Tensor;
+```
+
+## Test Plan
+
+- [x] batched_matmul: [4,8,32,64]×[4,8,64,32] → max_err 2.7e-7
+- [x] attention (non-causal): B=1,H=2,S=8,D=16 → max_err 4.5e-8
+- [x] attention (causal): B=1,H=2,S=16,D=32 → max_err 3.0e-8
+- [x] attention (causal, larger): B=2,H=4,S=64,D=64 → max_err 6.0e-8
+- [x] causal mask 语义: position 0 只能看到 token 0，output[0] == V[0] → exact
+
+## Takeaways
+
+1. **`to_device` 不应强制 contiguous**：最初 `to_device()` 会先调 `contiguous()`，而 GPU 的 `contiguous()` 又调 `to_device(Cpu)`，导致无限递归栈溢出。修复：`to_device()` 直接传输 raw storage，保留 strides/offset，用户需要时自己调 `contiguous()`。GPU `contiguous()` 现在走 GPU→CPU→CPU contiguous→CPU→GPU 路径——正确但低效，Phase 15 需要写 GPU contiguous kernel。
+
+2. **Batched GEMM via `cublasGemmStridedBatchedEx`**：row-major trick 同 Phase 3，额外参数是 stride（元素数，不是字节）。stride_a = M×K, stride_b = K×N, stride_c = M×N。注意初始版本错误地乘了 `elem_size`，cuBLAS 的 stride 单位是元素。
+
+3. **Attention 的组合式实现足够验证正确性**：没有写 fused kernel，而是复用 `batched_matmul` + `scale` + `causal_mask` + `softmax`。精度极好（max_err < 1e-7），因为每步都在 FP32 中完成。缺点是 S×S score 矩阵完全 materialize（O(S²) 显存），Flash Attention 会解决。
+
+4. **Scale kernel 的必要性**：原本想在 CPU 上做 scale（round-trip），但那太慢了。加了 `scale_f32/bf16` 逐元素 CUDA kernel。未来可以把 scale 合进 GEMM 的 alpha 参数，省一次 kernel launch。
+
+5. **Causal mask 的 offset 设计**：`col > row + offset` 中的 offset 为 KV cache 场景预留。Decode 时 Q 只有 1 行但 KV cache 有前 S 行，offset = kv_len - q_len 确保 decode query 能看到所有 cached tokens。
--- a/docs/06-model-loading.md
+++ b/docs/06-model-loading.md
@@ -0,0 +1,69 @@
+# Phase 6: Model Loading — Design Document
+
+## Goal
+
+从 HuggingFace safetensors 文件加载模型权重到 GPU Tensor。解析 config.json 获取模型结构参数。
+
+## Crate: `xserv-model`
+
+```
+crates/xserv-model/src/
+├── lib.rs
+├── config.rs       # ModelConfig from config.json
+├── loader.rs       # safetensors weight loading
+└── gpt2.rs         # (Phase 8) GPT-2 model definition
+```
+
+## Dependencies
+
+- `safetensors` crate: parse safetensors format
+- `serde` + `serde_json`: deserialize config.json
+- `memmap2`: mmap for zero-copy file access (safetensors uses this internally)
+
+## Weight Loading Flow
+
+```
+safetensors file (disk)
+  → safetensors crate parses header (tensor names, shapes, dtypes, offsets)
+  → mmap raw data
+  → for each tensor:
+      → read bytes at offset
+      → create CPU Tensor from raw bytes
+      → .to_device(Cuda(0)) → GPU Tensor
+  → return HashMap<String, Tensor>
+```
+
+## Config Parsing
+
+```rust
+#[derive(Deserialize)]
+pub struct ModelConfig {
+    pub architectures: Option<Vec<String>>,
+    pub model_type: Option<String>,
+    pub hidden_size: usize,
+    pub intermediate_size: Option<usize>,
+    pub num_attention_heads: usize,
+    pub num_key_value_heads: Option<usize>,
+    pub num_hidden_layers: usize,
+    pub vocab_size: usize,
+    pub max_position_embeddings: Option<usize>,
+    pub layer_norm_eps: Option<f64>,
+    pub rms_norm_eps: Option<f64>,
+    pub rope_theta: Option<f64>,
+    pub tie_word_embeddings: Option<bool>,
+}
+```
+
+## Test Plan
+
+- [x] Load GPT-2 124M: 160 tensors loaded successfully
+- [x] Parse GPT-2 config.json: hidden=768, layers=12, heads=12, vocab=50257
+- [x] Sharded loading path implemented (for larger models)
+
+## Takeaways
+
+1. **GPT-2 vs modern HF config naming**：GPT-2 uses `n_embd`/`n_head`/`n_layer`/`n_positions`，而不是 `hidden_size`/`num_attention_heads` 等。ModelConfig 需要支持两套命名并提供统一的 accessor methods（`hidden()`, `num_heads()` 等）。
+
+2. **safetensors 零拷贝读取**：`safetensors` crate 直接 mmap 文件，解析 header 得到 tensor 的 offset 和 shape，然后 zero-copy 读取 raw bytes。对于 GPT-2 的 500MB 权重文件，加载速度很快。
+
+3. **模型下载的网络问题**：HuggingFace 在中国网络下不可达。使用 modelscope.cn 或 hf-mirror.com 作为替代。大文件（>100MB）的 redirect 到 CDN 可能也会失败，modelscope 的 snapshot_download 更可靠。
--- a/docs/07-tokenizer.md
+++ b/docs/07-tokenizer.md
@@ -0,0 +1,57 @@
+# Phase 7: BPE Tokenizer — Design Document
+
+## Goal
+
+从零实现 Byte-Pair Encoding tokenizer，兼容 HuggingFace `tokenizer.json` 格式。支持 GPT-2 和 Qwen3。
+
+## Crate: `xserv-tokenizer`
+
+```
+crates/xserv-tokenizer/src/
+├── lib.rs
+├── bpe.rs          # BPE encode/decode core algorithm
+└── chat.rs         # Chat template formatting
+```
+
+## Dependencies
+
+- `serde` + `serde_json`: parse tokenizer.json
+- `regex`: pre-tokenization patterns
+
+## BPE Algorithm
+
+### Encode
+1. Pre-tokenize: split text by regex (GPT-2 pattern)
+2. Each word → byte sequence → initial token list (one token per byte)
+3. Repeatedly merge highest-priority pair until no more merges
+4. Map merged tokens to IDs via vocab
+
+### Decode
+Token IDs → lookup vocab → concatenate bytes → UTF-8 decode
+
+## Key Data Structures
+
+```rust
+pub struct Tokenizer {
+    vocab: HashMap<Vec<u8>, u32>,        // token bytes → ID
+    vocab_rev: Vec<Vec<u8>>,             // ID → token bytes
+    merges: Vec<(Vec<u8>, Vec<u8>)>,     // ordered merge rules
+    merge_ranks: HashMap<(u32, u32), usize>,  // (id_a, id_b) → priority
+    special_tokens: HashMap<String, u32>,
+    pre_tokenize_regex: Regex,
+}
+```
+
+## Test Plan
+
+- [x] Encode + decode roundtrip verified (GPT-2 tokenizer, English text)
+- [x] Special tokens handled (endoftext)
+- [x] Integrated into GPT-2 inference pipeline, generates coherent text
+
+## Takeaways
+
+1. **GPT-2 byte-to-unicode 映射**：GPT-2 的 vocab 中，每个 byte 都映射到一个 Unicode 字符。可打印 ASCII (0x21-0x7E) 映射到自身，其余字节（空格、控制字符等）映射到 U+0100 以上的 Unicode 码点。解码时需要反向映射。这个映射表是 BPE tokenizer 正确性的关键。
+
+2. **Rust regex 不支持 lookahead**：GPT-2 的 pre-tokenization regex 使用了 `(?!\S)` lookahead，Rust 的 `regex` crate 不支持。简化为去掉 lookahead 后功能等价（whitespace 仍然被正确分词）。如果需要精确匹配 Python 行为，需要 `fancy-regex` crate。
+
+3. **BPE merge 的 O(n²) 复杂度**：当前实现每次 merge 扫描整个 token 序列找最高优先级 pair，复杂度 O(n² × |merges|)。对于短文本够用，长文本需要 priority queue 优化。推理场景中 prompt 通常 < 10K tokens，暂时可接受。
--- a/docs/08-gpt2.md
+++ b/docs/08-gpt2.md
@@ -0,0 +1,71 @@
+# Phase 8: GPT-2 Complete Inference — Design Document (Milestone ①)
+
+## Goal
+
+Wire everything together: load GPT-2 124M, tokenize input, run forward pass, sample tokens, decode output. First time seeing the model "speak".
+
+## Model Architecture (GPT-2 124M)
+
+```
+hidden_size = 768
+num_heads = 12
+num_layers = 12
+vocab_size = 50257
+max_position_embeddings = 1024
+activation = GELU
+normalization = LayerNorm (pre-LN)
+tied embeddings (lm_head == wte)
+```
+
+## Forward Pass
+
+```
+tokens [S]
+  → wte[tokens] + wpe[0..S]           → [S, 768]
+  → for each layer:
+      residual = x
+      x = layernorm(x, ln_1)
+      x = attention(x)                 # Q,K,V from linear, MHA, output linear
+      x = x + residual
+      residual = x
+      x = layernorm(x, ln_2)
+      x = mlp(x)                       # linear→GELU→linear
+      x = x + residual
+  → layernorm(x, ln_f)
+  → logits = x @ wte.T                → [S, 50257]
+  → sample(logits[-1])                 → next token
+```
+
+## Sampling
+
+- Greedy: argmax
+- Temperature: logits / T → softmax → sample
+- Top-K: keep top-k logits, rest = -inf
+- Top-P: sorted by prob, cumsum ≤ p
+
+## CLI Binary
+
+```
+$ cargo run --release --bin xserv-cli -- --model path/to/gpt2
+
+xserv> The future of AI is
+GPT-2> ...generated text...
+```
+
+## Test Plan
+
+- [x] Greedy generation produces coherent English text
+- [x] Interactive CLI works (pipe and interactive mode)
+- [x] Multiple prompts verified: "The future of AI is", "Once upon a time"
+
+## Takeaways
+
+1. **QKV split + head reshape 的 layout 陷阱（最关键的 bug）**：GPT-2 的 `c_attn` 输出 `[S, 3H]` 需要 split 成 Q/K/V 再 reshape 成 `[1, num_heads, S, head_dim]`。关键错误：从 `[S, num_heads, head_dim]` 直接 `reshape` 到 `[1, num_heads, S, head_dim]` 不等于 transpose！Reshape 只是重新解释 flat data 的 shape，不会重排数据。必须手动按 `[batch, head, seq, dim]` 的目标 layout 写入数据。同理 merge_heads 也需要手动重排。
+
+2. **CPU round-trip 作为 correctness first 策略**：`add_tensors`、`add_bias`、`split_qkv`、`merge_heads` 都通过 CPU round-trip 实现。虽然慢（每次都有 GPU→CPU→GPU 拷贝），但确保了正确性。Phase 15 会写专门的 CUDA kernel 替换这些操作。
+
+3. **GPT-2 的 Conv1D 权重布局**：GPT-2 用 `Conv1D` 而非 `Linear`，权重存为 `[in, out]`（不是标准 Linear 的 `[out, in]`）。计算方式是 `x @ weight`（不需要转置）。这和 Qwen3/LLaMA 的 `[out, in]` 布局不同——Phase 10 需要注意。
+
+4. **Greedy decoding 的重复问题**：GPT-2 124M 在 greedy decoding 下极易陷入循环（"The world was a place of great danger, and..."）。这是已知行为，temperature + top-k/top-p sampling 可以缓解。当前实现只有 greedy，sampling 将在后续添加。
+
+5. **无 KV Cache 的性能代价**：每生成一个 token 都要重新跑完整 forward pass（O(S²) attention）。50 tokens 的生成需要 50 次 full forward，每次的 attention 复杂度还在增长。Phase 9 的 KV Cache 会将 decode 降到 O(S) per token。
Author	SHA1	Message	Date
Gahow Wang	e1e75fc7f6	phase 6+7+8: model loading, BPE tokenizer, GPT-2 inference (Milestone ①) Phase 6 — Model Loading (xserv-model): - safetensors parser with single/sharded file support - ModelConfig with dual naming (GPT-2 n_embd/n_head + modern HF naming) - Weight loading flow: safetensors → mmap → CPU Tensor → GPU Phase 7 — BPE Tokenizer (xserv-tokenizer): - Full BPE encode/decode from tokenizer.json - GPT-2 byte-to-unicode mapping (printable ASCII identity + shifted bytes) - Pre-tokenization regex, special token handling - Chat template support structure Phase 8 — GPT-2 Complete Inference: - GPT-2 model definition: wte, wpe, 12 transformer blocks, ln_f - Forward pass: embedding → (LayerNorm → MHA → residual → LayerNorm → MLP → residual) × 12 → LN → logits - QKV split with correct [batch, heads, seq, dim] layout (fixed reshape bug) - Greedy sampling from last-position logits - Interactive CLI: xserv-cli <model-dir> [--max-tokens N] Verified: GPT-2 124M generates coherent English text on RTX 5090. "The future of AI is uncertain. The future of AI is uncertain..." "Once upon a time, the world was a place of great beauty..." Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>	2026-05-21 22:04:00 +08:00
Gahow Wang	6035ffdc0b	phase 5: naive multi-head attention - Batched GEMM via cublasGemmStridedBatchedEx - Causal mask CUDA kernel (F32 + BF16) - Element-wise scale CUDA kernel (F32 + BF16) - attention() composing: batched_matmul + scale + causal_mask + softmax - Fixed to_device/contiguous infinite recursion (GPU contiguous via CPU round-trip) - 5 attention tests passing (max_err < 3e-7 F32) - Total: 61 tests passing across all crates Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>	2026-05-21 21:17:23 +08:00
Gahow Wang	c8e8153702	phase 4: transformer core kernels CUDA kernels (csrc/): - common.cuh: shared warp_reduce_sum/max, block_reduce_sum/max - normalization/rmsnorm.cu: RMSNorm (F32 + BF16) - normalization/layernorm.cu: LayerNorm with Welford (F32 + BF16) - activation/activations.cu: GELU tanh-approx + SiLU (F32 + BF16) - reduce/softmax.cu: safe softmax, 3-pass (F32 + BF16) - embedding/embedding.cu: gather lookup (F32 + BF16) - embedding/rope.cu: RoPE in-place + precomputed cos/sin cache (F32 + BF16) Rust wrappers (xserv-kernels/src/): - rmsnorm.rs, layernorm.rs, activation.rs, softmax.rs, embedding.rs, rope.rs - RopeCache struct with GPU-side precomputation Tests: 12 new tests (ops_test.rs), all passing with good precision: - F32: max_err 1e-6 ~ 1e-9 - BF16: max_err 2e-3 ~ 7e-3 Total: 29 kernel tests + 27 prior = 56 tests passing Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>	2026-05-21 21:07:24 +08:00
Gahow Wang	51a0f2eb14	docs: add design docs + takeaways for Phase 2 and Phase 3 - docs/01-cuda-ffi.md: added takeaways (struct layout pitfall, Rust 2024 unsafe changes, caching allocator strategy, etc.) - docs/02-tensor.md: design doc + takeaways for tensor abstraction - docs/03-gemm.md: design doc + takeaways for GEMM kernels Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>	2026-05-21 20:59:45 +08:00