[Bugfix][Perf][SM70/SM75] Widen QSA sparse launch profile to pre-Ampere - #469
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The GB300 prefill profiles select a 64-column tile that cannot launch on SM75 at D=256 (Triton OutOfResources against Turing's 64 KiB shared memory), and the existing SM70 retune does not apply there. Gate the branch on compute capability < 8.0 and pick the 16-column four-warp tile, which launches on both pre-Ampere architectures and measures 1.16-2.6x faster than the best previously runnable profile across the 64..2048-row prefill regimes (V100-PCIE-32GB, Quadro RTX 8000; 1CatAI#441). Small-batch decode profiles and the sm80+ table are unchanged. Co-authored-by: Claude <noreply@anthropic.com> Signed-off-by: Peuqui <peuqui@github.com>
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Validated against main after #466: merge is conflict-free; targeted QSA suites report 20 passed, 1 skipped; targeted pre-commit passes. The change remains a pre-Ampere fallback/profile improvement and does not override the grouped Page4 fast path.
…stream 1CatAI#469 Assisted-by: GLM (zai/glm-5.3-flash) Signed-off-by: Joker <joker@sabatech.dev>
Assisted-by: GLM (zai/glm-5.3-flash) Signed-off-by: Joker <joker@sabatech.dev>
…QSA tiles Own-measurement verification of the community claim (narrow 16-col tiles 19.3x vs GB300 profile on V100, D=256 TOPK2048 2048-token prefill): reproduced at 18.53x on our hardware. Run per-GPU via CUDA_VISIBLE_DEVICES. Assisted-by: GLM (zai/glm-5.3-flash) Signed-off-by: Joker <joker@sabatech.dev>
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Follow-up to #441, as requested there. Unlike the closed #455 (our dispatch mistake — apologies again), every number below was measured against this file (
nvidia/ops/qsa.pyat ca73a34) on both of our pre-Ampere cards.What
Widen the existing SM70 branch in
_qsa_sparse_launch_profileto all pre-Ampere devices and let it pick the narrow 16-column, four-warp tile:current_platform.is_device_capability(70)→not current_platform.has_device_capability(80)(SM80+ keeps the GB300 table bit-for-bit),block_n = 16, partial_warps = 4for every prefill regime (the branch only fires when the GB300 table choseblock_n == 64, so the small-batch decode profiles are untouched),Why
OutOfResourcesfor every prefill regime (rows ≥ 64 measured). The existing SM70 retune does not apply on SM75, and even force-applied it only helps ≥ 512 programs (N32) — the 33..256-program regimes keep N64 and still fail.Measurements
Production Qwen4Exp TP2 geometry (12 query heads, 1 KV head, D=256, TOPK=2048, PAGE_SIZE=16, bf16 caches, 16k-token KV), medians of 30 CUDA-event-timed calls after 3 warmups.
base_programs = rows(1 KV head).Tesla V100-PCIE-32GB (SM70):
Quadro RTX 8000 (SM75):
Methodology: the file at ca73a34 is loaded as-is via importlib and only
_qsa_sparse_launch_profileis overridden per data point, so launch, split merge and workspaces are exactly the shipped code paths. Every profile's output was cross-checked against the default profile's output — identical within bf16 split-reduction-order tolerance. With the patch applied, the default dispatch reproduces the N16 column on both cards.Decode is deliberately untouched: at rows 1/6/8 the GB300 table already picks the narrow high-split profiles, and they win (forcing S8 at rows=1 measured 3× slower). Also untouched:
sm70_single_tokeninqsa_mqa_paged, the TP4group_size == 6warp special case, and everything SM80+.Open question
Your N32 choice at ≥ 512 programs was tuned on the exact 512/8192-row shapes; on our cards N16 measures ahead of N32 there too (SM70 1.20×, SM75 1.16–1.17×). If you prefer to keep N32 on SM70, the minimal alternative is widening only the gate — but that leaves the 33..256-program regimes unable to launch on SM75, which is why this PR proposes N16 across the pre-Ampere prefill branch. Happy to rerun any shape you care about on V100-PCIE or RTX 8000.
Duplication check, tests, and AI assistance
Per the repository's agent guidelines:
gh pr list --state open --searchfor "qsa launch profile", "pre-ampere" and "441 in:body" each return only this PR. The related closed [Perf] Pre-Ampere tile profiles for the QSA prefill dispatch (#441) #455 was our own earlier attempt that measured the wrong file; this PR supersedes it as discussed in [Perf][SM70/SM75] Pre-Ampere tuning findings from a mixed Volta/Turing rig — QSA #441.python -m pytest tests/models/qwen4_exp/test_qsa_launch_profile.py tests/models/qwen4_exp/test_qsa_ops.py -v→ 18 passed (7 launch-profile cases + 11 ops tests, including every untouched one).Refs #441.
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