dash5, gpt-oss-20b FP8, warm-server vs llama.cpp MXFP4 (6 reps):
TP=2 TPOT 5.76-5.89 vs 7.42-8.45 ms (xserv 1.26-1.47x), TTFT 2.4x
ahead short/medium; TP=1 5.78-5.95 vs 2.80-3.22 ms (gap 2.5x -> 2.0x,
TTFT now ahead short/medium). GSM8K-50 through the graph path: 94%.
Lesson recorded: graphs bought ~0.6 ms (launches were already hidden
by async execution), the GPU argmax ~1 ms — measure, don't guess.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
- docs/19-gpt-oss-moe.md: the numbered series jumped 18->20; write up
gpt-oss arch deltas, harmony pitfalls, and the two CUDA debugging
postmortems (fully-masked-tile NaN in flash-attention sinks;
pre-__syncthreads early return reading uninitialized smem in the
decode GEMV) — the highest-value learning content of that phase.
- README: models/perf/capabilities were frozen at the Qwen3-only era;
now lists gpt-oss MoE, TP/PP, FP8/MXFP4, sparse MoE, and the
llama.cpp standing.
- Roadmap: record where reality diverged from the plan at Phase 18+,
add milestone entries and the ranked next-phase candidates
(21 CUDA-graph MoE decode, 22 non-expert quant, 23 sparse prefill).
- sparse-moe benchmark doc: post-review-fix numbers.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Dense MoE replicated x across all 16 local experts and ran the full
batched GEMM, reading every expert's weights per token; the weighted
sum then discarded 12 of 16 results. Decode is memory-bound, so this
was ~8x wasted expert bytes — the entire decode gap vs llama.cpp.
New fused expert-indexed GEMVs (csrc/moe/moe_sparse.cu) read
topk_ids on-device (no host sync) and early-return block-uniformly
for experts other ranks own. FP8 runs W8A16 (activations stay BF16 —
tensor cores are irrelevant at M=1, and activation quantization error
disappears); MXFP4 runs W4A16. Per-expert bias + scale fused into the
GEMV epilogue; slot-indexed weighted sum skips (never multiplies)
unwritten non-local slots. Dense path retained for num_tokens > 8
(prefill) and via XSERV_DENSE_MOE=1 for A/B.
dash5 (RTX 5090), gpt-oss-20b FP8, TP=2: decode TPOT 13.9 -> 7.6 ms.
Warm-server vs llama.cpp MXFP4 TP=2: TPOT 7.19-7.32 vs 7.54-8.42 ms —
first config where xserv wins decode outright. GSM8K-100: 96% (dense
FP8: 91%). llama TP=1 (2.9 ms) remains ahead: next levers are decode
CUDA graphs, non-expert quantization, sparse prefill (docs/20).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
