The optimized path grouped warp lanes by token and required
warp_size % n_expert_used == 0, with a single hardcoded exception
padding 6 up to 8. Every other count fell back to the generic path,
which walks the tokens one at a time with a warp reduction per token,
for each of the n_expert blocks.
The lane group only has to divide the warp, and the loop body already
guards the padded lanes with iex < n_expert_used, so the padding
generalizes to the next power of two. The 6 -> 8 case and every count
already dispatched keep the exact same padding as before.
n_expert_used = 10 now reaches the fast path. Measured on
Qwen3.8-Flash-Next (512 experts, 10 used) at 55k context on an
RTX PRO 6000, warm runs with the first one discarded:
prompt processing 2334 -> 2600 t/s
Token generation is unaffected, since a single token leaves nothing to
walk. Other expert counts reach the fast path by adding their case to
the dispatch.
* CUDA: dedup MoE gate/up activation quantization (fp4)
For MoE gate/up projections the src1 activation is broadcast across the
routed experts (ne11 == 1), so ids_src1 maps every one of a token's
n_expert_used slots to the same physical row. The MMQ path therefore
re-quantized each token's activation n_expert_used times.
For fp4 (NVFP4/MXFP4) src0, quantize each unique token row once instead of
once per expert. For NVFP4 a single quantize+scatter kernel
(quantize_scatter_mmq_nvfp4) quantizes each token once and writes the
resulting block_fp4_mmq straight to all n_expert_used slots, using an
inverse token->compact-row map (build_tok2c). MXFP4, and
GGML_CUDA_MOE_QUANT_GATHER=1, use a two-kernel variant: quantize unique
rows then gather into the expert-sorted layout (gather_mmq_fp4_blocks).
Both are bit-identical to the previous gather-then-quantize path (identical
source data, deterministic per-block quantization), verified by
test-backend-ops MUL_MAT_ID (type_a=nvfp4, broadcast b=1; 790/790 for the
default, gather, and per-expert paths) and by coherent end-to-end
generation. Set GGML_CUDA_NO_MOE_QUANT_DEDUP=1 to force the original
per-expert path.
Same-binary A/B on RTX 5090 (sm_120), Qwen3.6-35B-A3B-NVFP4 prefill @8192
(nsys, graphs-off; the unchanged mul_mat_q GEMM confirms stable clocks):
activation-quant GPU-busy drops 61% (78.2 -> 30.4 ms) with the fused
quantize+scatter, vs 33% (78.2 -> 52.8 ms) for the two-kernel gather. The
fused path avoids materializing and re-reading the 8x compact buffer,
writing the expert copies directly from registers.
* CUDA: bounds-check token ids in build_tok2c_kernel
Guard against malformed ids_src1: skip out-of-range token ids (t < 0 or
t >= n_tokens) and drop entries beyond n_expert_used per token instead of
writing past the token's tok2c region. No behavior change for valid MoE
routing data; test-backend-ops MUL_MAT_ID 790/790.
* Refactor the code based on review comments
- Removed previously added kernels that were not necessary anymore\
- Added an inverse mapping from (token, slot) to compact row. Each token is quantized once and scattered to its compact rows.
* Adding q8_1 support for dedup and addressing review comments
* Add pragma unrolls
* Remove redundant cudaMemsetAsync call
* Removing follow up redundancies
---------
Co-authored-by: praneshgo <227579474+praneshgo@users.noreply.github.com>
Pascal