[Build] DeepGEMM pin has no SM120 kernels: family-12 Blackwell cannot run hyperconnections

[Mirrdhyn]

The problem

DeepGEMM dispatches the TF32 hyperconnection pre-norm GEMM on the device arch major, in
csrc/apis/hyperconnection.hpp. At the revision this repository pins,
vllm-project/DeepGEMM e21c821, that dispatch handles arch_major 9 and 10 only:

const auto arch_major = device_runtime->get_arch_major();
if (arch_major == 9) {
    sm90_tf32_hc_prenorm_gemm(...);
} else if (arch_major == 10) {
    sm100_tf32_hc_prenorm_gemm(...);
} else {
    DG_HOST_UNREACHABLE("Unsupported architecture");
}

That revision ships no sm120_* implementation at all. csrc/jit_kernels/impls/
contains sm90_* and sm100_* only. tools/install_deepgemm.sh currently comments
that the pin targets nv-dev "due to sm120 support", but the pinned tree does not carry
it.

So every SM120/SM121 device aborts as soon as a model exercises hyperconnections.
DeepSeek-V4 Flash is one: it is configured with hc_mult=4, so the path is hit on the
first forward pass.

The change

Points both pins at deepseek-ai/DeepGEMM a6b593d, which carries sm120_bf16_gemm,
sm120_bmk_bnk_mn, sm120_fp8_fp4_gemm_1d1d and sm120_tf32_hc_prenorm_gemm, and
whose dispatch has the arch_major == 12 branch.

cmake/external_projects/deepgemm.cmake and tools/install_deepgemm.sh both document
that they must stay in sync, so both are updated. To be explicit: only the cmake path
is exercised by my build; the install_deepgemm.sh edit is the same two values kept
in sync, but I have not run that script.

Testing

With this change, DeepSeek-V4-Flash-0731 builds and serves on 2× NVIDIA GB10 (SM121,
aarch64, CUDA 13.2, torch 2.13.0+cu132) with --tensor-parallel-size 2 across two
nodes. That is the configuration currently running here, and the fetched tree does
contain the four sm120_* kernels.

The failure itself does not really need a reproduction, since it is visible in the
pinned tree: csrc/apis/hyperconnection.hpp at e21c821 has no arch_major == 12
branch, and csrc/jit_kernels/impls/sm120_tf32_hc_prenorm_gemm.hpp does not exist at
that revision. For the record, we did hit DG_HOST_UNREACHABLE("Unsupported architecture") on the old pin before switching, but I no longer have that log and am
not claiming a fresh reproduction. Note it is a runtime abort rather than a build
error: DeepGEMM JIT-compiles its kernels, so the build succeeds and the process dies
on the first forward pass reaching the dispatch.

Recipe, scripts and raw measurements from that setup:
https://github.com/Mirrdhyn/dsv4-flash-dgx-spark

Caveat, and a question for maintainers

This is the minimal change that demonstrably fixes SM12x, but it may not be the change
you want.

The two hyperconnection kernels shared by both trees are byte-identical
(sm90_tf32_hc_prenorm_gemm.hpp c17d1b5, sm100_tf32_hc_prenorm_gemm.hpp
0071e2c), so the hyperconnection path itself is unaffected on SM90 and SM100. Other
kernels have diverged, however: sm90_bf16_gemm.hpp differs between the two revisions,
which suggests the fork carries vLLM-specific work that repointing would drop. I have
no SM90 or SM100 hardware and have not tested those architectures.

If the fork does carry changes worth keeping, the better fix is to port the sm120_*
kernels into vllm-project/DeepGEMM, or to rebase the fork onto a newer upstream, and
leave the pin where it is. I am happy to redo the patch that way. Either path is fine
by me; the point of this PR is that SM12x is currently broken and the fix is small.

[claude]

Claude Code Review

This pull request is from a fork — automated review is disabled. A repository maintainer can comment @claude review to run a one-time review.

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