[Bugfix][DSv4] SM12x Triton fallback for fp8_einsum / o_proj (#43743)

[ajwharton]

Purpose

Fixes #43743.

We're trying to intuit where you are already going on SM12x / GB10 and help
out with a small, reviewable slice — not a parallel stack.

On current main, DSv4 o_proj always calls DeepGEMM fp8_einsum.
compute_fp8_einsum_recipe() treats cap.major >= 10 as the SM100
(1, 1, 128) layout. GB10 / RTX 50 report major=12, so they take that
recipe and die on the first forward (layout.hpp scale-factor assert —
the same class as "Unknown SF transformation").

#41834 already fixed tf32_hc_prenorm_gemm. This PR is the follow-up
pasta-paul described in #43743: port jasl's Triton SM12x fp8_einsum
fallback and dispatch it with a per-kernel predicate (capability,
equation, recipe, scale dtype), not support_deep_gemm() |= family(120).

That last point is deliberate. We tried the blunt family-120 DeepGEMM
enable on a dual GB10 box; MoE selected DEEPGEMM_MXFP4, then linear
o_proj hit layout.hpp:97. The gate comment on CudaPlatform was
right. This PR does not open that gate.

What this does / does not

Does:

• SM12x uses the SM90-shaped recipe (1, 128, 128) + Triton fallback
• SM100 path is unchanged
• CPU dispatch tests lock the predicate so SM12x cannot select the
  SM100 recipe

Does not:

• Enable DeepGEMM MoE on SM12x
• Claim end-to-end DeepSeek-V4-Flash serve
• Replace or rebase [New Model][Nvidia] Add SM12x support for DeepSeek V4 Flash with essential fixes #41834

Attribution

• Triton kernel: jasl/vllm (PR [New Model][Nvidia] Add SM12x support for DeepSeek V4 Flash with essential fixes #41834 preview), Apache-2.0
• Issue + port plan: [DSv4] [SM 12.0] fp8_einsum has no SM 12.0 fallback — blocks mainline serve on consumer Blackwell (follow-up to #41834) #43743 (pasta-paul)
• Dispatch invariant: AasthaPJoshi on [DSv4] [SM 12.0] fp8_einsum has no SM 12.0 fallback — blocks mainline serve on consumer Blackwell (follow-up to #41834) #43743 (per-kernel capability
  predicates, not architecture-family assumptions)

We are integrators/validators on GB10 (DGX Spark). Draft while we attach
a silicon log from a single-node sm_121 probe (synthetic o_proj tensors;
no 156G load). Happy to adjust the predicate or split the kernel file if
that's a better fit for how you want this to land.

Test Plan

pytest tests/models/test_dsv4_sm12x_fp8_einsum_dispatch.py -q

GB10 kernel probe (synthetic bhr,hdr->bhd, recipe (1,128,128)) still
in flight — will comment the log on this PR.

Test Result

Dispatch tests exist; not yet run in CI. Silicon evidence forthcoming.

---

• Purpose linked to [DSv4] [SM 12.0] fp8_einsum has no SM 12.0 fallback — blocks mainline serve on consumer Blackwell (follow-up to #41834) #43743
• Test plan
• Test results (draft until GB10 probe + CI)
• No docs change needed (existing DSv4 path)

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[ajwharton]

GB10 silicon log (single-node, synthetic)

Draft update: ran the Triton fallback on a live DGX Spark (NVIDIA GB10, compute capability (12, 1)) inside official vllm/vllm-openai:latest = vLLM 0.27.1, with only the two PR files bind-mounted.

torch 2.13.0+cu130
device NVIDIA GB10
device_capability (12, 1)
recipe (1, 128, 128) tma_aligned_scales False
predicate_sm12x_recipe True predicate_sm100_recipe False
out_finite True out_absmax 28.75
max_abs_err_vs_fp32_ref 0.05612945556640625
PROBE_OK

Same window, same image: Qwen2.5-VL-3B served on that GB10 (system_fingerprint vllm-0.27.1-5143e9e3), text chat returned Pong. Then restored the node's production container.

This is the o_proj / fp8_einsum contract only — not an end-to-end DeepSeek-V4-Flash claim. Dual-node DS4 on this image is the next measurement.

[ajwharton]

DCO should be green on 409086a5f (Signed-off-by: Andrew Wharton <ajwharton@gmail.com>).

pre-run-check is the first-author label gate (0 merged PRs; needs verified / ready / ready-run-all-tests). We cannot self-label. Happy to wait for a maintainer to apply that if you want pre-commit to run.

GB10 silicon log is in the previous comment.

[maci0]

Field report from 2x DGX Spark GB10 (SM 12.1), TP=2, deepseek-ai/DeepSeek-V4-Flash-0731.

compute_fp8_einsum_recipe() treating cap.major >= 10 as SM100 packed INT32 is the bug we hit. GB10 reports major 12, so fused_inv_rope_fp8_quant emitted packed UE8M0 and o_proj became noise.

This PR's SM12x recipe (1, 128, 128) / tma_aligned_scales=False is the right split. Main still has the major <= 9 / else SM100 branch.

On this box Triton w8a8_triton_block_scaled_mm dies with KeyError: 'float8_e8m0fnu', so we used B12x linear plus a Python dequant fp8_einsum fallback with the same SM90-shaped recipe. Isolated einsum is fine. Live greedy "The capital of France is" (temperature=0, max_tokens=32) is " Paris. The capital of Spain is Madrid...", first token ' Paris' logprob -0.244.

Happy to re-test this branch on the same pair if useful.

[TurboTheTurtle]

End-to-end GB10 follow-up on current head 409086a5f588d155ffbddd4bb7b917c96333ed3c.

I used this PR's two runtime files byte-for-byte in a vLLM 0.27.1 adaptation:

• fp8_einsum.py: 176421dff581a957520445305d2443473cb044772901792cb765fd96d6556b35
• o_proj.py: 085142bd5d8742c3e5ca5a3d4dd96901226e85acbe2044f49e263bb489601172

The serving test was 2× DGX Spark / GB10 (SM121), TP=2, with an FP4 DeepSeek-V4-Flash-0731 checkpoint, MXFP4 B12X experts, FlashInfer sparse MLA, NVFP4 DS-MLA KV, probabilistic DSpark k=5, 532,288 max context, and CUDA graphs.

The full model loaded 79.48 GiB per rank, allocated 746,430 KV tokens, completed sparse-MLA autotuning and graph capture, and reached API readiness. A six-part functional run passed model listing, thinking-off, reasoning, exact tool-call JSON, streaming, and 48,033-token retrieval. Both ranks remained restart-zero and OOM-free, with no Xid, CUDA/NCCL fatal, EngineDeadError, traceback, or failed post-readiness response.

Scope note: this validates the two runtime files from this PR as part of a complete SM12x serving stack, not the PR's test file or a standalone cherry-pick. Additional SM12x MHC/MQA and FlashInfer sparse-MLA shape fixes were also required for the full serve.

[ajwharton]

Closing this draft. Decision made 2026-08-23: upstream vLLM is continuing down the SM12x/DeepGEMM path on its own, so this fork-side Triton-fallback slice is no longer worth maintaining. The commit (and full fork history) is preserved in a local bundle. Thanks to jasl/#41834 and #43743 for the groundwork — we'll pick this up through official channels when it matures.

[maci0]

Main still takes the SM100 packed-INT32 recipe whenever cap.major >= 10, so GB10 (major 12) still packs UE8M0. We are not reviving the Triton fp8_einsum path here (torch.float8_e8m0fnu dies on this stack).

Recipe-only follow-up: #53521