gahow/kvcache-simulator
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Update README with full feature documentation

Browse Source 
Cover all 11 routing policies (including new prefix_affinity, cache_load,
cache_score, estimated_ttft, least_tokens), HuggingFace config.json
auto-parsing, GPU hardware presets, architecture-aware compute model
(MoE/MLA/DSA/GQA), router parameter tuning, bundled model configs and
config files, and available traces.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Gahow Wang
2026-04-14 01:21:28 +08:00
parent ec73a95e05
commit 8d41123418
1 changed files with 222 additions and 44 deletions
Download Patch File Download Diff File Expand all files Collapse all files

264
README.md
View File

@@ -8,6 +8,26 @@ ablate routing strategies and cache sizing without spinning up any GPUs.
Assumes **PD (prefill/decode) disaggregation** — only the prefill path is Assumes **PD (prefill/decode) disaggregation** — only the prefill path is
modeled. modeled.
## Features
- **Architecture-derived roofline compute** — auto-derives FLOPs,
attention coefficients, and weight-streaming costs from model
architecture (MoE, MLA, GQA, DSA, sliding window).
- **HuggingFace config.json auto-parsing** — drop in any HF
`config.json` and the simulator extracts layer counts, attention heads,
MoE expert configs, MLA LoRA ranks, and DSA sparse parameters.
- **Built-in GPU hardware presets** — H100, H800, H20, A100-80GB,
A100-40GB, B200 with tensor-parallel scaling (e.g. `8xb200`).
- **Two-tier KV cache hierarchy** — L0 (GPU HBM) + L1 (CPU DRAM) with
LRU eviction and cross-instance RDMA fetch via a cluster-wide
meta-store.
- **11 routing policies** — from baselines (random, round-robin) to
cache-aware (min\_pd, prefix\_affinity) for systematic ablation.
- **Token-bucket link contention** — PCIe and RDMA bandwidth modeled with
reservation-based token-bucket queues.
- **Oracle analysis** — computes theoretical hit-rate ceilings (infinite
cache, Belady optimal, LRU) for gap analysis.
## Build ## Build
```bash ```bash
@@ -26,7 +46,7 @@ git submodule update --init --recursive
### 1. Run a single simulation ### 1. Run a single simulation
```bash ```bash
target/release/kvcache-sim run --config configs/qwen2.5-coder-7b-h800.yaml target/release/kvcache-sim run --config configs/glm5-8xb200-hf.yaml
``` ```
Prints `summary.json` to stdout and writes the full output directory Prints `summary.json` to stdout and writes the full output directory
@@ -36,29 +56,28 @@ Prints `summary.json` to stdout and writes the full output directory
```bash ```bash
target/release/kvcache-sim ablate \ target/release/kvcache-sim ablate \
--config configs/qwen2.5-coder-7b-h800.yaml \ --config configs/glm5-8xb200-hf.yaml \
--num-instances 64 \ --routers random,least_loaded,least_tokens,min_pd,prefix_affinity \
--output-dir runs/qwen7b_n64 \ --output-dir runs/glm5_ablation
--routers random,least_loaded,ttl_aware,precise
``` ```
Writes one subdirectory per router plus a combined Writes one subdirectory per router plus a combined
`runs/qwen7b_n64/ablation.json` with side-by-side summaries. `ablation.json` with side-by-side summaries.
### 3. Compute theoretical hit-rate ceilings (oracle) ### 3. Compute theoretical hit-rate ceilings (oracle)
```bash ```bash
# Cluster-aggregate capacity (default) # Cluster-aggregate capacity (default)
target/release/kvcache-sim oracle \ target/release/kvcache-sim oracle \
--config configs/qwen2.5-coder-7b-h800.yaml --num-instances 64 --config configs/glm5-8xb200-hf.yaml --num-instances 64
# A single instance's HBM budget # A single instance's HBM budget
target/release/kvcache-sim oracle \ target/release/kvcache-sim oracle \
--config configs/qwen2.5-coder-7b-h800.yaml --per-instance --config configs/glm5-8xb200-hf.yaml --per-instance
# Explicit capacity in 16-token blocks # Explicit capacity in blocks
target/release/kvcache-sim oracle \ target/release/kvcache-sim oracle \
--config configs/qwen2.5-coder-7b-h800.yaml --capacity-blocks 200000 --config configs/glm5-8xb200-hf.yaml --capacity-blocks 200000
``` ```
Reports three numbers: Reports three numbers:
@@ -74,7 +93,7 @@ only reachable by adding capacity.
### 4. Validate a config without running ### 4. Validate a config without running
```bash ```bash
target/release/kvcache-sim validate --config configs/qwen2.5-coder-7b-h800.yaml target/release/kvcache-sim validate --config configs/glm5-8xb200-hf.yaml
``` ```
Parses the YAML, prints derived per-instance block budgets, and dumps Parses the YAML, prints derived per-instance block budgets, and dumps
@@ -102,15 +121,179 @@ and `--out <PATH>`. `ablate` additionally takes `--routers <csv>`.
Set `cluster.router.mode` in the YAML or list in `--routers`: Set `cluster.router.mode` in the YAML or list in `--routers`:
| Mode | What it does | | Mode | Aliases | What it does |
|----------------|--------------------------------------------------------------------| |-------------------|------------------|--------------------------------------------------------------------------------------|
| `random` | Uniform random. Baseline. | | `random` | | Uniform random. Baseline. |
| `round_robin` | Deterministic round-robin. Baseline. | | `round_robin` | `rr` | Deterministic round-robin. Baseline. |
| `least_loaded` | `argmin(kv_blocks_used + alpha * queue_len)`. KV-blind. | | `least_loaded` | | `argmin(kv_blocks_used + alpha * queue_len)`. KV-blind load balance. |
| `ttl_aware` | Picks instance with longest prefix in the global TTL meta store. | | `least_tokens` | `lt` | `argmin(waiting_tokens)`. Pure load balance by queued compute work. |
| `precise` | Probes top-K least-loaded instances' actual caches; charges probe latency into TTFT. | | `ttl_aware` | `ttl` | Picks instance with longest prefix in the global TTL meta-store. Cache-only. |
| `precise` | `precise_aware` | Probes top-K least-loaded instances' actual caches; charges probe latency into TTFT. |
| `min_pd` | `minpd`, `pd` | Minimizes `P*D` (prefill tokens x ongoing requests). Cluster-wide RDMA-aware. |
| `cache_load` | `cl` | Filters to least-loaded 1/4 instances, then picks best cache prefix. |
| `cache_score` | `cs` | Exponential scoring: `2^(alpha * queue_len + beta * miss_blocks)`. |
| `estimated_ttft` | `ettft`,`optimal`| Estimates `drain_time + fetch_time` per instance using architecture-aware compute. |
| `prefix_affinity` | `affinity`, `pa` | Rendezvous-hashed prefix fingerprinting for deterministic cache locality. |
Expected hit-rate ordering: `random ≲ least_loaded ≲ ttl_aware ≲ precise`. ### Router parameters
These fields in `cluster.router` tune specific routers:
| Field | Default | Used by | Description |
|--------------------------|---------|------------------|------------------------------------------------------|
| `load_alpha` | `1.0` | `least_loaded` | Weight of queue\_len vs kv\_blocks\_used |
| `score_alpha` | `1.0` | `cache_score` | Load weight in `2^(alpha*load + beta*miss)` |
| `score_beta` | `0.1` | `cache_score` | Cache-miss weight in `2^(alpha*load + beta*miss)` |
| `prefix_k` | `8` | `prefix_affinity`| Number of leading blocks for the prefix fingerprint |
| `affinity_fan_out` | `0` | `prefix_affinity`| Top-K affinity candidates (0 = auto: n/8, min 2) |
| `precise_probe_latency_us`| `50.0`| `precise` | Simulated per-probe latency (microseconds) |
| `precise_probe_topk` | `4` | `precise` | Number of instances probed |
### Router design spectrum
```
Cache-only Hybrid Load-only
(hot-spot risk) (cache-blind)
┌─────────┬───────────┬───────────┬────────────┬───────────┬───────────┐
ttl_aware precise cache_score min_pd prefix_ least_ random
cache_load affinity loaded
est_ttft least_tokens
```
`prefix_affinity` sits in a unique position: it builds **proactive cache
locality** by consistently routing same-prefix requests to the same
instances (via rendezvous hashing), rather than reactively chasing
existing cache state. This yields the highest L0 hit rates while
maintaining load balance through within-group drain-time-aware selection.
## Model configuration
### HuggingFace config.json (recommended)
Point `model.config_json` at any HF `config.json` to auto-extract
architecture:
```yaml
model:
config_json: ../models/GLM-5/config.json
dtype_bytes: 2 # required (not in HF schema)
block_size_tokens: 512 # required (not in HF schema)
```
Auto-detected features:
| Feature | Detection trigger | What it extracts |
|-----------|-------------------------------|----------------------------------------------|
| **MoE** | `n_routed_experts`, `num_local_experts`, or `num_experts` | Expert count, active experts, shared experts, expert FFN width |
| **MLA** | `kv_lora_rank` present | KV/Q LoRA ranks, qk\_rope/nope dims, v\_head\_dim |
| **DSA** | `first_k_dense_replace` present| Dense window, sparse stride, first dense layers |
| **Sliding window** | `sliding_window` present | Window size |
| **GQA** | `num_key_value_heads < num_attention_heads` | KV head count for grouped-query attention |
Explicit YAML fields always override the auto-detected values.
### Inline specification
Alternatively, specify architecture fields directly:
```yaml
model:
name: qwen2.5-coder-7b
num_layers: 28
hidden_size: 3584
num_attention_heads: 28
num_kv_heads: 4
head_dim: 128
intermediate_size: 18944
dtype_bytes: 2
block_size_tokens: 16
```
When `hidden_size` is present, the compute model is auto-derived
(architecture mode). Without it, you must supply legacy manual
coefficients (`flops_per_token_prefill`, `attn_quadratic_coeff`, etc.).
### Bundled model configs
| Model | Path | Architecture |
|-------|------|--------------|
| GLM-5 (744B/40B-active) | `models/GLM-5/config.json` | MoE (256 routed, 8 active, 1 shared) + MLA + DSA |
| Qwen3-Coder-480B-A35B FP8 | `models/Qwen3-Coder-480B-A35B-Instruct-FP8/config.json` | MoE (160 experts, 8 active) + GQA |
## Hardware configuration
### Using presets (recommended)
Set `hardware.type` to a preset name — individual fields can override:
```yaml
hardware:
type: 8xb200
hbm_bytes: 500.0e9 # override KV budget (after model weights)
```
Available presets:
| Preset | FLOPS | HBM | Mem BW | PCIe |
|-------------|------------|---------|------------|------|
| `h100` | 989 TFLOPS | 80 GB | 3.35 TB/s | Gen5 |
| `h800` | 989 TFLOPS | 80 GB | 3.35 TB/s | Gen5 |
| `h20` | 148 TFLOPS | 96 GB | 4.0 TB/s | Gen5 |
| `a100-80gb` | 312 TFLOPS | 80 GB | 2.0 TB/s | Gen4 |
| `a100-40gb` | 312 TFLOPS | 40 GB | 1.555 TB/s | Gen4 |
| `b200` | 2.25 PFLOPS| 192 GB | 8.0 TB/s | Gen6 |
Prefix with `2x`, `4x`, or `8x` for tensor-parallel groups (e.g.
`8xh20`). FLOPS, memory bandwidth, and HBM scale linearly; RDMA and
DRAM are set to sensible per-node defaults.
### Inline specification
```yaml
hardware:
gpu_flops: 1.80e16
gpu_mem_bw: 6.40e13
hbm_bytes: 500.0e9
dram_bytes: 1.5e12
pcie_bw: 128.0e9
pcie_latency_us: 4.0
rdma_bw: 50.0e9
rdma_latency_us: 6.0
max_batch_slots: 256
prefill_chunk_tokens: 4096
```
## Architecture-aware compute model
The simulator derives a **roofline prefill model** from model
architecture:
```
prefill_time(N tokens) = max(compute_time, memory_time)
compute_time = layers * (N * linear_flops + attn_coeff * N * effective_ctx(N)) / gpu_flops
memory_time = layers * weight_bytes_per_layer / gpu_mem_bw
```
- **MoE**: only active experts contribute to FLOPs and weight streaming
(shared experts always counted)
- **MLA**: compressed KV projections reduce attention FLOPs; KV cache
uses `kv_lora_rank + qk_rope_head_dim` instead of `2 * kv_heads * head_dim`
- **DSA**: `effective_ctx = min(N, dense_window) + max(0, N - dense_window) / sparse_stride`,
with the first K layers using full dense attention
- **GQA**: fewer KV heads reduce both attention compute and KV cache size
## Bundled config files
| Config | Model | Hardware | Instances | Trace |
|--------|-------|----------|-----------|-------|
| `glm5-8xb200-hf.yaml` | GLM-5 via HF config.json | 8xB200 preset | 32 | GLM coder blk512 |
| `glm5-8xb200-blk512.yaml` | GLM-5 inline | 8xB200 inline | 64 | GLM coder blk512 |
| `glm5-8xb200.yaml` | GLM-5 inline | 8xB200 inline | 8 | GLM coder blk512 |
| `qwen3-coder-480b-8xh20.yaml` | Qwen3-Coder via HF | 8xH20 preset | 32 | Qwen coder blk16 |
| `qwen2.5-coder-7b-h800.yaml` | Qwen2.5-7B inline | H800 inline | 16 | Qwen coder blk16 |
| `qwen2.5-coder-7b-preset.yaml` | Qwen2.5-7B inline | H800 preset | 16 | Qwen coder blk16 |
| `qwen2.5-coder-32b-h800.yaml` | Qwen2.5-32B inline | H800 inline | 16 | Qwen coder blk16 |
## Outputs ## Outputs
@@ -130,39 +313,33 @@ For `oracle`: an `oracle.json` with the three hit-rate analyses.
```bash ```bash
# Pretty-print the summary # Pretty-print the summary
cat runs/qwen7b/summary.json | jq . cat runs/glm5_8xb200_hf/summary.json | jq .
# Compare all routers from an ablation # Compare all routers from an ablation
cat runs/qwen7b_n64/ablation.json | jq '.[] | {router, ttft_p50, hit_rate_l0, total_rdma_bytes}' cat runs/glm5_8xb200_hf/ablation.json | \
jq '.[] | {router, ttft_mean, ttft_p50, hit_rate_l0, miss_rate}'
# Hit-rate ceilings vs LRU at the same capacity # Sort by TTFT
cat runs/qwen7b/oracle.json | jq '{unlimited: .unlimited.hit_rate, belady: .belady_finite.hit_rate, lru: .lru_finite.hit_rate}' cat runs/glm5_8xb200_hf/ablation.json | \
jq 'sort_by(.ttft_mean) | .[] | {router, ttft_mean, hit_rate_l0}'
``` ```
## Config
A config is a single YAML file with four sections. A working example
lives at
[`configs/qwen2.5-coder-7b-h800.yaml`](configs/qwen2.5-coder-7b-h800.yaml);
copy and edit for other models/hardware.
```yaml
model: # shape + prefill roofline coefficients
hardware: # per-instance GPU/PCIe/RDMA capabilities + batch knobs
cluster: # num_instances, meta_store TTL, router mode
sim: # trace_path, max_requests, output_dir, seed
```
Only prefill-side model coefficients are used; any decode fields in
legacy YAMLs are accepted and ignored.
## Trace format ## Trace format
The simulator reads the Alibaba The simulator reads the Alibaba
[`qwen-bailian-usagetraces-anon`](https://github.com/alibaba-edu/qwen-bailian-usagetraces-anon) [`qwen-bailian-usagetraces-anon`](https://github.com/alibaba-edu/qwen-bailian-usagetraces-anon)
JSONL schema. Each record has `chat_id`, `timestamp`, `input_length`, JSONL schema. Each record has `chat_id`, `timestamp`, `input_length`,
`output_length`, and `hash_ids` (16-token block hashes). Only the `output_length`, and `hash_ids` (block hashes, typically 16 tokens each).
input side is used. Only the input side is used.
Available traces in the submodule:
| Trace | Requests | Description |
|-------|----------|-------------|
| `qwen_coder_blksz_16.jsonl` | 43k | Qwen Coder serving traffic |
| `qwen_traceA_blksz_16.jsonl` | 43k | Qwen general traffic A |
| `qwen_traceB_blksz_16.jsonl` | 173k | Qwen general traffic B |
| `qwen_thinking_blksz_16.jsonl` | 11k | Qwen reasoning/thinking traffic |
## Testing ## Testing
@@ -170,5 +347,6 @@ input side is used.
cargo test --release cargo test --release
``` ```
16 tests: 15 unit + 1 smoke that runs all four routers on a synthetic 28 tests: 27 unit tests (compute model, HF config parsing, hardware
presets) + 1 integration smoke test that runs routers on a synthetic
shared-prefix trace and asserts the expected hit-rate ordering. shared-prefix trace and asserts the expected hit-rate ordering.