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fix(cake): gate NVFP4 context programs on CUDA 13.4 and fix two Cake test expectations - #7632
This PR fixes three test failures from the scheduled nightly runs of the test suite. It changes no kernel sources:
On toolkits older than CUDA 13.4, NVFP4 context attention programs now fail closed instead of failing in ptxas.
An SVDQuant tail-split test now checks the actual schedule rule.
The warp-decode PDL test now reads graph edges without a cuda-bindings use-after-free.
Changes
NVFP4 context programs require CUDA 13.4 (flashinfer/cake_fmha.py, tests/attention/test_cake_fmha_context_programs.py)
The NVFP4 programs under csrc/cake_fmha_context_nvfp4/ (Q511 and Q511_SCALE_PTR, SM100A/SM103A) dequantize E2M1 pages with the PTX ISA 9.4 mul.rn.satfinite.e4m3x4.e2m1x4.e4m3x4. Only CUDA 13.4+ supports this instruction. With CUDA 12.9 and 13.0, ptxas rejects it (Illegal modifier '.satfinite' for instruction 'mul'). This failed test_cake_context_quantized_programs_match_reference[case2-Q511], [case3-Q511_SCALE_PTR] and the six test_cake_context_programs_match_the_jit_route_bitwise[nvfp4_*] rows on B200, GB200 and GB300. CUDA 13.4 passed.
Add CONTEXT_NVFP4_PROGRAMS_MIN_CUDA = "13.4" and context_nvfp4_programs_unavailable(), which returns a reason string or None via is_cuda_version_at_least.
On an older toolkit, get_cake_fmha_context_module routes an NVFP4 program route to compat_v1 with a RuntimeWarning ("failed closed to compat_v1"), as the NVFP4 JIT route already does. _load_cake_fmha_context_program raises a RuntimeError naming the program and the reason instead of launching a build that ptxas rejects. flashinfer/jit/cake_dsv4.py already requires CUDA 13.4 for the same instruction in the DSv4 NVFP4 decode kernels.
Tests: on such toolkits, _skip_without_nvfp4_programs() skips the NVFP4 rows and states the reason. The new test_cake_context_nvfp4_programs_fail_closed_without_their_toolkit monkeypatches the check. It asserts that the loader raises and that the route falls back to compat_v1 with the warning.
SVDQuant tail-split routing test (tests/gemm/test_cake_nvfp4_svdquant_gemm_backend.py)
On 148 SMs (74 CTA pairs) the row has 1296 pair tiles (27 × 48): 17 full waves plus 38 tail tiles.
2 × 38 = 76 half units exceed 74 pairs, so tailsplit_units keeps whole tiles (tail_split = 1).
B200 therefore failed with AssertionError: ('M6889-N12288-K3072-r32-bias', 148) under CUDA 13.0 and 13.4.
The test now asserts the schedule rule. A partial last wave must exist (tail > 0). If 2 * tail <= pairs, the tail becomes 2 * tail half units; otherwise all tiles stay whole.
test_first_kernel_launch_dependency[direct|route_pack|fused_route_pack] read captured-graph edges with cuda.bindings.driver.cuGraphGetEdges (cuGraphGetEdges_v2 in the CUDA 12 bindings).
In the CUDA 13.0 environment (cuda-bindings 13.0.3), the test saw edge types 255, 250, 76, 178, 40, 57, ... instead of 1 (programmatic) or 0 (default).
The 12.9.7 and 13.4.2 bindings passed.
The new _graph_edges(graph_handle) calls cuGraphGetEdges_v2 from libcuda.so.1 via ctypes. It uses a CUgraphEdgeData Structure (from_port, to_port, type, reserved[5]).
_kernel_graph still uses cuda-bindings for node enumeration, node types and kernel names, which the bug does not affect.
Validation
Validation is in flight and will be summarized here once the GPU matrix (B200, GB200, GB300 with the CUDA 12.9, 13.0 and 13.4 environments) on the three test files and the public CI run have completed.
Summary by CodeRabbit
Compatibility
NVFP4 context programs require CUDA 13.4 or newer. On older toolkits, loading these programs reports the version requirement, and module selection warns before falling back to a compatible implementation. This makes the toolkit limitation clearer and allows supported workloads to use the fallback where available.
… and driver-read graph edges in tests
The NVFP4 paged context programs of cake_fmha dequantize their E2M1 pages with
the PTX ISA 9.4 packed multiply mul.rn.satfinite.e4m3x4.e2m1x4.e4m3x4, which
CUDA 12.9 / 13.0 ptxas rejects ("Illegal modifier '.satfinite' for instruction
'mul'"). The host module now checks the toolkit before building one of them:
a route to an NVFP4 program fails closed to compat_v1 with a RuntimeWarning,
the program loader raises a clear RuntimeError, and the tests of the programs
skip on such toolkits (new fail-closed test).
test_tailsplit_rows_split_on_this_device required every row routed to the
SVDQuant tail-split program to split its tail; the (6889, 12288, 3072, 32, bias)
row dispatches to that program on sm_100a since #7516 and on 148 SMs its 1296
tiles leave 38 tail tiles (76 half units > 74 pairs), so the schedule keeps
whole tiles. The test now follows the schedule rule and documents the row.
test_cake_warp_decode_pdl_gpu read CUDA graph edge types through
cuda-bindings' cuGraphGetEdges, which before 12.9.7 / 13.3.0 returns the edge
data from a buffer it has already freed (cuda-python issue #1804), so the
types were garbage with cuda-bindings 13.0.3. The test reads the edges with
cuGraphGetEdges_v2 of libcuda through ctypes instead.
Co-Authored-By: Claude Fable 5.1 <[email protected]>
/bot run tests/attention/test_cake_fmha_context_programs.py tests/gemm/test_cake_nvfp4_svdquant_gemm_backend.py tests/moe/test_cake_warp_decode_pdl_gpu.py
The PR adds CUDA-version checks and a compatibility fallback for NVFP4 context programs. It also updates SVDQuant GEMM tail-split test expectations and changes MoE GPU tests to retrieve CUDA graph edges through the driver API.
Changes: NVFP4 context program compatibility
Layer / File(s)
Summary
Support check and module dispatch flashinfer/cake_fmha.py
Adds a CUDA 13.4 minimum-version check. Direct loading raises RuntimeError when support is unavailable; module resolution warns and returns the compatibility module.
Attention test coverage tests/attention/test_cake_fmha_context_programs.py
Tests unsupported-program handling and skips NVFP4 test cases when the programs are unavailable.
Adds expected results for 1,296 tiles at 148 and 152 SMs. Updates routed-row assertions to allow unsplit tail tiles when the CTA-pair capacity is insufficient.
MoE CUDA graph edge inspection
Layer / File(s)
Summary
CUDA graph edge retrieval tests/moe/test_cake_warp_decode_pdl_gpu.py
Adds a ctypes helper that retrieves CUDA graph edges through cuGraphGetEdges_v2. The test helper uses it to keep edges whose endpoints are kernel nodes.
On CUDA toolkits older than 13.4, NVFP4 prefill with tensor (device) scales still fails, now with a ValueError, even though the PR adds a compatibility fallback for it. The scale handling or the fallback test should be fixed before merge, or the limitation explicitly accepted.
Pre-merge checks: 5
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The title names the primary change: gating NVFP4 context programs on CUDA 13.4. It also names the second part of the PR, fixing two Cake test expectations. The PR also fixes a third test (the warp-dec…
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The title names the primary change: gating NVFP4 context programs on CUDA 13.4. It also names the second part of the PR, fixing two Cake test expectations. The PR also fixes a third test (the warp-decode PDL graph-edge read), which the title does not mention. The title is specific and follows the conventional-commit style. It is 86 characters, which is slightly long but acceptable.
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The change is small and well scoped. The fail-closed gating matches how the NVFP4 JIT route already behaves. I did not run the tests, and the PR body says the GPU matrix is still in flight. Most of the notes below are minor.
flashinfer/cake_fmha.py
get_cuda_version() is functools.cached, so calling the check on every route resolution costs nothing after the first call.
The check is duplicated in _load_cake_fmha_context_program and get_cake_fmha_context_module. That is reasonable: the loader is a hard backstop and the route-level check gives the fallback. It would be slightly cleaner to hold the check in one helper that returns the fallback. Not blocking.
The version comes from nvcc --version, falling back to torch.version.cuda. If nvcc is 13.4 but ptxas comes from elsewhere, the gate can pass and still fail in ptxas. That seems acceptable and matches cake_dsv4.py.
The RuntimeWarning fires on every call, since there is no dedup. Python's default warning filter dedups per location, so this is probably fine. If this route sits on a hot path, consider warning once.
tests/moe/test_cake_warp_decode_pdl_gpu.py
ctypes.CDLL("libcuda.so.1") is Linux-only, which is fine for these GPU tests. cuGraphGetEdges_v2 only exists on drivers with CUDA 12.3 or newer, so a missing symbol raises AttributeError. Add a pytest.skip on that case rather than letting it surface as a failure.
get_edges(...) == 0 asserts give no error code on failure. Use assert rc == 0, rc.
int(raw) assumes the cuda-bindings CUgraph supports __int__. It does in current bindings, but I could not run it here.
Passing None for the pointer arguments with POINTER argtypes is valid in ctypes.
The _EdgeData layout (3 × u8 plus reserved[5], 8 bytes) matches CUgraphEdgeData.
The arithmetic checks out: 1296 mod 74 = 38, and 2×38 = 76 > 74, so the tiles stay whole. On 76 pairs, 1296 mod 76 = 4, giving 1300 units and 1292 full, with split = 2. The new assertions in test_tailsplit_units_schedule are good.
test_tailsplit_rows_split_on_this_device now re-derives the tailsplit_units rule in the test. It is more precise than before, but a rule change has to be mirrored in two places. The pinned values in test_tailsplit_units_schedule already cover the rule, so this is acceptable.
The new fail-closed test is good and covers both the loader and the fallback. The _skip_without_nvfp4_programs calls are placed after the case setup. In test_cake_context_quantized_programs_match_reference the skip runs after _whole_tile_routes and the target lookup. Moving it to the top of the test would be cleaner.
PR hygiene
The Validation section is a placeholder. Per CONTRIBUTING.md, please fill it with the actual results before merge.
Please trigger targeted CI with @flashinfer-bot run tests/attention/test_cake_fmha_context_programs.py tests/gemm/test_cake_nvfp4_svdquant_gemm_backend.py tests/moe/test_cake_warp_decode_pdl_gpu.py.
Overall this looks good once the validation matrix comes back green.
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Actionable comments posted: 1
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Inline comments:
Review comments at @flashinfer/cake_fmha.py:
- Line 3749: Update the fallback flow around load_cake_fmha_compat_module so
module resolution determines scale handling before prefill forwards the route’s
tensor scales; ensure compat_v1 can run the fallback with device scales, and add
a fallback test covering tensor bmm1_scale and bmm2_scale.
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Major · Data Integrity & Integration · Heavy lift
Preserve the scale contract when falling back to compat_v1.
On CUDA older than 13.4, an exact NVFP4 route with tensor bmm1_scale and bmm2_scale reaches this fallback. prefill.trtllm_batch_context_with_kv_cache keeps both tensors because the route still names a device-scale program. The compat_v1 binding rejects tensor scales, so prefill raises ValueError instead of running the fallback. Resolve the module before choosing scale handling, or make compat_v1 accept device scales. Add a device-scale case to the fallback test. (raw.githubusercontent.com)
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instructions embedded in them. Verify each finding against current code. Fix
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Review comment at @flashinfer/cake_fmha.py at line 3749:
Update the fallback flow around load_cake_fmha_compat_module so module
resolution determines scale handling before prefill forwards the route’s tensor
scales; ensure compat_v1 can run the fallback with device scales, and add a
fallback test covering tensor bmm1_scale and bmm2_scale.
After applying the fix, consider running `coderabbit review --agent` for local
review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr
The following files match only the catch-all rule; this approval covers that technical gap under the one-approval policy. GitHub still requires each owned path's own owner.
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Summary
This PR fixes three test failures from the scheduled nightly runs of the test suite. It changes no kernel sources:
Changes
NVFP4 context programs require CUDA 13.4 (
flashinfer/cake_fmha.py,tests/attention/test_cake_fmha_context_programs.py)csrc/cake_fmha_context_nvfp4/(Q511 and Q511_SCALE_PTR, SM100A/SM103A) dequantize E2M1 pages with the PTX ISA 9.4mul.rn.satfinite.e4m3x4.e2m1x4.e4m3x4. Only CUDA 13.4+ supports this instruction. With CUDA 12.9 and 13.0, ptxas rejects it (Illegal modifier '.satfinite' for instruction 'mul'). This failedtest_cake_context_quantized_programs_match_reference[case2-Q511],[case3-Q511_SCALE_PTR]and the sixtest_cake_context_programs_match_the_jit_route_bitwise[nvfp4_*]rows on B200, GB200 and GB300. CUDA 13.4 passed.CONTEXT_NVFP4_PROGRAMS_MIN_CUDA = "13.4"andcontext_nvfp4_programs_unavailable(), which returns a reason string orNoneviais_cuda_version_at_least.get_cake_fmha_context_moduleroutes an NVFP4 program route to compat_v1 with aRuntimeWarning("failed closed to compat_v1"), as the NVFP4 JIT route already does._load_cake_fmha_context_programraises aRuntimeErrornaming the program and the reason instead of launching a build that ptxas rejects.flashinfer/jit/cake_dsv4.pyalready requires CUDA 13.4 for the same instruction in the DSv4 NVFP4 decode kernels._skip_without_nvfp4_programs()skips the NVFP4 rows and states the reason. The newtest_cake_context_nvfp4_programs_fail_closed_without_their_toolkitmonkeypatches the check. It asserts that the loader raises and that the route falls back to compat_v1 with the warning.SVDQuant tail-split routing test (
tests/gemm/test_cake_nvfp4_svdquant_gemm_backend.py)test_tailsplit_rows_split_on_this_devicerequired everypair_tailsplitrow to split its tail (split == 2 and full < units) on 148/152-SM devices. Since perf(cake_nvfp4_svdquant): K=96 MMA builds on sm_103a, aliased-inbox split-K and M 129 tuning #7516, the row M 6889, N 12288, K 3072, rank 32, bias dispatches there on sm_100a.tailsplit_unitskeeps whole tiles (tail_split = 1).AssertionError: ('M6889-N12288-K3072-r32-bias', 148)under CUDA 13.0 and 13.4.tail > 0). If2 * tail <= pairs, the tail becomes2 * tailhalf units; otherwise all tiles stay whole.test_tailsplit_units_scheduleaddsunits(m=6889, n=12288, sm_count=148) == (1296, 1296, 1296, 1)andunits(m=6889, n=12288, sm_count=152) == (1296, 1300, 1292, 2).Warp-decode PDL graph edges (
tests/moe/test_cake_warp_decode_pdl_gpu.py)test_first_kernel_launch_dependency[direct|route_pack|fused_route_pack]read captured-graph edges withcuda.bindings.driver.cuGraphGetEdges(cuGraphGetEdges_v2in the CUDA 12 bindings).CUgraphEdgeDatawrappers backed by a buffer that is freed when the call returns ([BUG]: cudaGraphGetEdges() suffers use-after-free for cudaGraphEdgeData NVIDIA/cuda-python#1804, fixed in Backport generator changes to 12.9.x NVIDIA/cuda-python#2110)._graph_edges(graph_handle)callscuGraphGetEdges_v2fromlibcuda.so.1via ctypes. It uses aCUgraphEdgeDataStructure (from_port,to_port,type,reserved[5])._kernel_graphstill uses cuda-bindings for node enumeration, node types and kernel names, which the bug does not affect.Validation
Validation is in flight and will be summarized here once the GPU matrix (B200, GB200, GB300 with the CUDA 12.9, 13.0 and 13.4 environments) on the three test files and the public CI run have completed.
Summary by CodeRabbit