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fix(jit): GEMM kernels produce NaN under concurrency — missing GDC flags cause PDL synchronization barriers to compile as no-ops #2716

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Merged
yzh119 merged 1 commit into from
Mar 9, 2026
+15 −1
Merged

fix(jit): GEMM kernels produce NaN under concurrency — missing GDC flags cause PDL synchronization barriers to compile as no-ops #2716

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16 changes: 15 additions & 1 deletion flashinfer/jit/gemm/core.py
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Original file line number Diff line number Diff line change
Expand Up @@ -91,6 +91,8 @@ def gen_gemm_sm100_module_cutlass_fp4() -> JitSpec:
+ [
"-DENABLE_BF16",
"-DENABLE_FP4",
"-DCUTLASS_ENABLE_GDC_FOR_SM100=1",
"-DCUTLASS_ENABLE_GDC_FOR_SM90=1",
],
Comment on lines 91 to 96
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@gemini-code-assist gemini-code-assist bot Mar 7, 2026

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medium

To improve maintainability and reduce code duplication, consider defining these new GDC (Grid Dependency Control) compile flags as a constant list at the module level. This constant can then be reused across all the JIT spec generation functions that require these flags, as this pattern is repeated in 5 other places in this file.

For example, you could define the following at the top of flashinfer/jit/gemm/core.py:

GDC_COMPILE_FLAGS = [
    "-DCUTLASS_ENABLE_GDC_FOR_SM100=1",
    "-DCUTLASS_ENABLE_GDC_FOR_SM90=1",
]

And then use it as suggested below.

        + [
            "-DENABLE_BF16",
            "-DENABLE_FP4",
        ] + GDC_COMPILE_FLAGS

extra_cflags=[
"-DFAST_BUILD",
Expand Down Expand Up @@ -158,6 +160,8 @@ def gen_gemm_sm103_module_cutlass_fp4() -> JitSpec:
+ [
"-DENABLE_BF16",
"-DENABLE_FP4",
"-DCUTLASS_ENABLE_GDC_FOR_SM100=1",
"-DCUTLASS_ENABLE_GDC_FOR_SM90=1",
],
Comment on lines 160 to 165
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medium

To avoid code duplication, please use the GDC_COMPILE_FLAGS constant as suggested in the previous comment.

        + [
            "-DENABLE_BF16",
            "-DENABLE_FP4",
        ] + GDC_COMPILE_FLAGS

extra_cflags=[
"-DFAST_BUILD",
Expand Down Expand Up @@ -206,6 +210,8 @@ def gen_gemm_sm120_module_cutlass_fp4() -> JitSpec:
+ [
"-DENABLE_BF16",
"-DENABLE_FP4",
"-DCUTLASS_ENABLE_GDC_FOR_SM100=1",
"-DCUTLASS_ENABLE_GDC_FOR_SM90=1",
],
Comment on lines 210 to 215
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medium

To avoid code duplication, please use the GDC_COMPILE_FLAGS constant as suggested.

        + [
            "-DENABLE_BF16",
            "-DENABLE_FP4",
        ] + GDC_COMPILE_FLAGS

extra_cflags=[
"-DFAST_BUILD",
Expand Down Expand Up @@ -256,6 +262,8 @@ def gen_gemm_sm100_module_cutlass_fp8() -> JitSpec:
extra_cuda_cflags=nvcc_flags
+ [
"-DENABLE_BF16",
"-DCUTLASS_ENABLE_GDC_FOR_SM100=1",
"-DCUTLASS_ENABLE_GDC_FOR_SM90=1",
],
Comment on lines 263 to 267
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medium

To avoid code duplication, please use the GDC_COMPILE_FLAGS constant as suggested.

        + [
            "-DENABLE_BF16",
        ] + GDC_COMPILE_FLAGS

extra_cflags=[
"-DFAST_BUILD",
Expand Down Expand Up @@ -349,6 +357,8 @@ def gen_gemm_sm100_module_cutlass_mxfp8() -> JitSpec:
extra_cuda_cflags=nvcc_flags
+ [
"-DENABLE_BF16",
"-DCUTLASS_ENABLE_GDC_FOR_SM100=1",
"-DCUTLASS_ENABLE_GDC_FOR_SM90=1",
],
Comment on lines 358 to 362
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medium

To avoid code duplication, please use the GDC_COMPILE_FLAGS constant as suggested.

        + [
            "-DENABLE_BF16",
        ] + GDC_COMPILE_FLAGS

extra_cflags=[
"-DFAST_BUILD",
Expand Down Expand Up @@ -516,7 +526,11 @@ def gen_gemm_sm120_module() -> JitSpec:
return gen_jit_spec(
"gemm_sm120",
source_paths,
extra_cuda_cflags=nvcc_flags,
extra_cuda_cflags=nvcc_flags
+ [
"-DCUTLASS_ENABLE_GDC_FOR_SM100=1",
"-DCUTLASS_ENABLE_GDC_FOR_SM90=1",
],
Comment on lines +529 to +533
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medium

To avoid code duplication, please use the GDC_COMPILE_FLAGS constant as suggested.

        extra_cuda_cflags=nvcc_flags + GDC_COMPILE_FLAGS

)


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