Samremes/zero init splitk#2
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Fix a custom-op contract bug that corrupted generation on the fused BlockScale SplitK zero-init path. The *_blockscale_splitk ops were registered mutates_args=["output"] but also returned `output`, so infer_schema declared a fresh (non-aliasing) return while the impl handed back the mutated buffer. Inductor trusted the schema, treated the output buffer as dead after the call, and reused it for the next block's zero-init prologue -- clobbering the still-live result (manifests with >=2 chained fused GEMM blocks). Make the splitk ops pure in-place (return None); the fusion pass already routes consumers through the mutated SSA edge, so the buffer stays live and Inductor cannot reuse it. Includes the fusion pass + producer/gemm ops, unit tests, and the repro/bench/diagnostic scripts for the fusion. Verified: multi-block reproducer (nb=1..4) passes with default Inductor buffer reuse (previously corrupted at nb>=2); direct custom-op contract check passes; pass unit tests 11/12 (the one failure is a pre-existing aiter gemma fused_qk_rmsnorm_group_quant type-check, unrelated). Co-authored-by: Cursor <cursoragent@cursor.com>
Rewrite non-stand-alone commentary in the blockscale SplitK zero-init
fusion sources so each comment/docstring reads as standalone technical
rationale for a reviewer with no knowledge of the original investigation.
- Drop references to a private codebase ("ATOM"), internal PR numbers,
and investigation-era phase/producer labels (P1..P4, "Phase-2").
- Remove quoted experimental results (microsecond costs, tuning-sweep CSV
paths) and investigation narrative ("regression guard against an earlier
bug", "reproduces the error from server boot").
- Reword the remaining rationale (e.g. why the split-K ops must mutate
output in place and never return/alias it) as plain standalone text.
Comment/docstring (and a couple of assert-message) text only; no code,
identifiers, or logic changed.
Co-authored-by: Cursor <cursoragent@cursor.com>
Drops the AITER_DEBUG_* tensor-tracing helper module and the call sites that were wired into the FP8 block-scale GEMM and quantization paths, restoring those functions to their upstream form. The zero-init SplitK fusion does not depend on this instrumentation. Co-authored-by: Cursor <cursoragent@cursor.com>
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…litk Co-authored-by: Cursor <cursoragent@cursor.com> # Conflicts: # vllm/config/compilation.py
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Pull request overview
This PR adds a ROCm/AITER-only compilation pass to fuse blockscale FP8 GEMM SplitK output zero-initialization into upstream producer kernels, reducing standalone zero-fill work before SplitK GEMMs.
Changes:
- Adds
fuse_blockscale_splitk_zero_initpass configuration and pass-manager integration. - Registers new AITER custom ops for zero-init-capable producers and preallocated-output SplitK GEMMs.
- Adds FX rewrite logic, ROCm-focused tests, and benchmark/debug tooling for Qwen3-Next FP8 scenarios.
Reviewed changes
Copilot reviewed 20 out of 20 changed files in this pull request and generated 5 comments.
Show a summary per file
| File | Description |
|---|---|
vllm/config/compilation.py |
Adds the new pass flag and ROCm-only validation. |
vllm/compilation/passes/pass_manager.py |
Wires the new fusion pass into the ROCm AITER pass pipeline. |
vllm/compilation/passes/fusion/blockscale_splitk_zero_init.py |
Implements producer/GEMM registries, pattern builders, rewrite logic, logging, and debug dumps. |
vllm/_aiter_ops.py |
Adds mutating zero-init producer ops and preallocated-output SplitK GEMM custom ops/accessors. |
tests/compile/passes/test_zero_init_dyn_shapes.py |
Adds dynamic-shape compile coverage for zero-init producer ops. |
tests/compile/passes/test_blockscale_splitk_zero_init.py |
Adds unit coverage for registry import, gating, rewrites, and attribution. |
benchmarks/run_vllm_qwen3_next_zero_init_demo.sh |
Adds end-to-end serving benchmark sweep for zero-init fusion modes. |
benchmarks/run_vllm_qwen3_next_serve_isl1024.sh |
Adds serving benchmark script for ISL/OSL 1024 workloads. |
benchmarks/run_vllm_qwen3_next_profile_master_csv.sh |
Adds profiling benchmark against a production tuned CSV. |
benchmarks/run_vllm_qwen3_next_profile_fse_compare.sh |
Adds FSE ablation profiling on top of the fusion. |
benchmarks/run_vllm_qwen3_next_profile_final.sh |
Adds final profiling benchmark configuration. |
benchmarks/run_vllm_qwen3_next_profile_demo.sh |
Adds short profiler verification sweep. |
benchmarks/run_vllm_qwen3_next_long_trace.sh |
Adds long steady-state trace capture script. |
benchmarks/run_runtime_splitk_reproducer.sh |
Adds shell wrapper for runtime SplitK reproducer. |
benchmarks/parse_zero_init_demo_results.py |
Adds profiler/benchmark result parser. |
benchmarks/diagnose_blockscale_splitk_fusion.sh |
Adds diagnostic server boot script with FX dumps. |
benchmarks/debug_vllm_runtime_splitk_reproducer.py |
Adds staged multi-block runtime correctness reproducer. |
benchmarks/debug_splitk_zero_init_correctness.py |
Adds direct custom-op correctness checker. |
benchmarks/debug_mini_vllm_splitk_zero_init_graph.py |
Adds minimal vLLM pass-pipeline reproducer. |
benchmarks/analyze_long_trace.py |
Adds long-trace analysis utility. |
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| return self.hash_source( | ||
| self, | ||
| ProducerSpec, | ||
| GemmSpec, | ||
| BlockScaleSplitKZeroInitFusionPass, | ||
| _make_2_input_producer_pattern, | ||
| _make_per_token_producer_pattern, | ||
| build_default_registries, | ||
| ) |
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| and len(user.args) >= 2 | ||
| and user.args[1] == 2 | ||
| ): |
| assert quant_dtype in [torch.int8, FP8_DTYPE] | ||
|
|
||
| out_shape = x.shape | ||
| out = torch.empty(x.shape, dtype=FP8_DTYPE, device=x.device) |
| ) -> tuple[torch.Tensor, torch.Tensor]: | ||
| out_shape = x.shape | ||
| return ( | ||
| torch.empty(x.shape, dtype=FP8_DTYPE, device=x.device), |
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| out, scale = torch.ops.vllm.rocm_aiter_gemma_rmsnorm_fp8_group_quant( | ||
| x, self.weight, EPS, GROUP_SIZE | ||
| ) |
…, Gemma test kwargs - uuid(): hash all registered pattern builders + _make_extra_check so a source change to any builder invalidates the Inductor compiled-graph cache. - Attribution walk: derive the zero-init buffer's getitem index per producer (functional-output count) instead of hardcoding 2, so the residual producer (buffer at index 3) is attributed correctly in the match table. - per_token_quant_with_zero_init (real + fake): allocate the output with quant_dtype instead of always FP8, matching rocm_aiter_per_token_quant. - Gemma producer test: call the op with kwargs to match the all-kwargs call shape built by _make_2_input_producer_pattern. Co-authored-by: Cursor <cursoragent@cursor.com>
These zero-init SplitK benchmark, profiling, and debug/repro scripts are local development tooling and should not be merged to main. Untracked via `git rm --cached` so the files remain in the working tree for local use. Co-authored-by: Cursor <cursoragent@cursor.com>
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| x_node = prod_node.args[0] if prod_node.args else None | ||
| if not isinstance(x_node, fx.Node): | ||
| return True |
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| if K < 2048: | ||
| return False |
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| try: | ||
| gemm_a8w8_blockscale( | ||
| A, | ||
| B, | ||
| As, | ||
| Bs, | ||
| dtype=output_dtype, | ||
| y=output, | ||
| split_k=split_k, | ||
| ) | ||
| except TypeError: | ||
| gemm_a8w8_blockscale(A, B, As, Bs, dtype=output_dtype, y=output) |
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