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Remove _CCCL_GRID_CONSTANT from scan kernel - #9854

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Remove _CCCL_GRID_CONSTANT from scan kernel#9854
bernhardmgruber wants to merge 1 commit into
NVIDIA:mainfrom
bernhardmgruber:fix_scan_reg

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@bernhardmgruber

@bernhardmgruber bernhardmgruber commented Jul 14, 2026

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Fixes: #9851

@bernhardmgruber
bernhardmgruber requested a review from a team as a code owner July 14, 2026 11:54
@github-project-automation github-project-automation Bot moved this to Todo in CCCL Jul 14, 2026
@cccl-authenticator-app cccl-authenticator-app Bot moved this from Todo to In Review in CCCL Jul 14, 2026
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coderabbitai Bot commented Jul 14, 2026

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No actionable comments were generated in the recent review. 🎉

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Reviewing files that changed from the base of the PR and between 22e4e68 and f29ec53.

📒 Files selected for processing (1)
  • cub/cub/device/dispatch/kernels/kernel_scan.cuh
📝 Walkthrough

Summary by CodeRabbit

  • Bug Fixes
    • Improved compatibility and reliability for device-wide scan operations across supported CUDA environments.
    • Standardized scan kernel argument handling to prevent compilation or execution issues related to parameter qualifiers.

Walkthrough

The scan initialization and execution kernel signatures in kernel_scan.cuh remove _CCCL_GRID_CONSTANT qualifiers from their parameters while retaining plain const declarations.

Changes

Scan kernel signature updates

Layer / File(s) Summary
Update scan kernel signatures
cub/cub/device/dispatch/kernels/kernel_scan.cuh		 DeviceScanInitKernel and DeviceScanKernel remove _CCCL_GRID_CONSTANT from their parameters, including the CUDA-version-conditional qualifier around init_value.

Assessment against linked issues

Objective Addressed Explanation
Fix the scan_exclusive_sum regression in CCCL 3.4 on Ampere [#9851] ❓ The signature changes appear related, but the provided changes do not include a test or explicit Ampere-specific validation confirming the regression is fixed.

Possibly related PRs

  • NVIDIA/cccl#9829: Removes the same kernel parameter qualifier from a related CUB dispatch kernel.
  • NVIDIA/cccl#9852: Applies the same _CCCL_GRID_CONSTANT removal pattern to related dispatch kernels.

Suggested reviewers: srinivasyadav18, davebayer, griwes

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@elstehle

elstehle commented Jul 14, 2026

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#9851 lists the Ampere regressions/fix. How does this PR influence behaviour on other architectures, e.g., look-ahead-enabled ones? Asking, because, I've previously seen both directions with _CCCL_GRID_CONSTANT annotations added/removed.

@bernhardmgruber

bernhardmgruber commented Jul 14, 2026

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That's a fair point. I only benchmarked that this PR mitigates the regression on Ampere. I did not check the impact on other architectures.

Here is CCCL 3.4 vs this PR on A100:

## [0] NVIDIA A100 80GB PCIe

|  T{ct}  |  OffsetT{ct}  |  Elements{io}  |   Ref Time |   Ref Noise |   Cmp Time |   Cmp Noise |       Diff |   %Diff |  Status  |
|---------|---------------|----------------|------------|-------------|------------|-------------|------------|---------|----------|
|   I8    |      I32      |      2^16      |  10.340 us |       3.97% |  10.322 us |       4.11% |  -0.019 us |  -0.18% |  🔵 SAME  |
|   I8    |      I32      |      2^20      |  15.418 us |      14.77% |  15.310 us |       8.17% |  -0.108 us |  -0.70% |  🔵 SAME  |
|   I8    |      I32      |      2^24      |  69.668 us |       1.99% |  69.675 us |       2.08% |   0.007 us |   0.01% |  🔵 SAME  |
|   I8    |      I32      |      2^28      | 936.423 us |       0.31% | 938.353 us |       0.32% |   1.930 us |   0.21% |  🔵 SAME  |
|   I8    |      I64      |      2^16      |  10.625 us |       4.99% |  10.544 us |       4.60% |  -0.081 us |  -0.77% |  🔵 SAME  |
|   I8    |      I64      |      2^20      |  15.669 us |      20.31% |  15.388 us |      12.84% |  -0.281 us |  -1.79% |  🔵 SAME  |
|   I8    |      I64      |      2^24      |  81.028 us |       1.20% |  81.214 us |       1.23% |   0.186 us |   0.23% |  🔵 SAME  |
|   I8    |      I64      |      2^28      |   1.128 ms |       0.25% |   1.129 ms |       0.22% |   0.742 us |   0.07% |  🔵 SAME  |
|   I8    |      I64      |      2^32      |  17.893 ms |       0.16% |  17.906 ms |       0.17% |  12.848 us |   0.07% |  🔵 SAME  |
|   I16   |      I32      |      2^16      |  11.027 us |       4.41% |  11.025 us |       4.52% |  -0.001 us |  -0.01% |  🔵 SAME  |
|   I16   |      I32      |      2^20      |  16.985 us |      11.30% |  17.089 us |      10.94% |   0.104 us |   0.61% |  🔵 SAME  |
|   I16   |      I32      |      2^24      |  87.541 us |       1.21% |  87.598 us |       1.18% |   0.057 us |   0.06% |  🔵 SAME  |
|   I16   |      I32      |      2^28      |   1.181 ms |       0.32% |   1.183 ms |       0.32% |   1.838 us |   0.16% |  🔵 SAME  |
|   I16   |      I64      |      2^16      |  10.884 us |       5.16% |  10.887 us |       4.79% |   0.002 us |   0.02% |  🔵 SAME  |
|   I16   |      I64      |      2^20      |  15.509 us |       2.94% |  15.561 us |       2.83% |   0.052 us |   0.33% |  🔵 SAME  |
|   I16   |      I64      |      2^24      |  85.391 us |       1.45% |  85.566 us |       1.63% |   0.175 us |   0.21% |  🔵 SAME  |
|   I16   |      I64      |      2^28      |   1.183 ms |       0.29% |   1.179 ms |       0.31% |  -3.791 us |  -0.32% |  🟢 FAST  |
|   I16   |      I64      |      2^32      |  18.777 ms |       0.16% |  18.723 ms |       0.16% | -54.027 us |  -0.29% |  🟢 FAST  |
|   I32   |      I32      |      2^16      |  10.971 us |       4.40% |  10.947 us |       4.72% |  -0.024 us |  -0.22% |  🔵 SAME  |
|   I32   |      I32      |      2^20      |  18.291 us |       3.31% |  18.340 us |       3.00% |   0.049 us |   0.27% |  🔵 SAME  |
|   I32   |      I32      |      2^24      | 108.340 us |       1.99% | 108.534 us |       1.95% |   0.194 us |   0.18% |  🔵 SAME  |
|   I32   |      I32      |      2^28      |   1.514 ms |       1.04% |   1.514 ms |       1.11% |  -0.026 us |  -0.00% |  🔵 SAME  |
|   I32   |      I64      |      2^16      |  11.044 us |       4.23% |  10.969 us |       4.55% |  -0.075 us |  -0.68% |  🔵 SAME  |
|   I32   |      I64      |      2^20      |  17.855 us |       3.81% |  18.065 us |       4.63% |   0.209 us |   1.17% |  🔵 SAME  |
|   I32   |      I64      |      2^24      | 105.971 us |       2.12% | 105.965 us |       2.16% |  -0.005 us |  -0.01% |  🔵 SAME  |
|   I32   |      I64      |      2^28      |   1.505 ms |       0.68% |   1.505 ms |       0.72% |  -0.101 us |  -0.01% |  🔵 SAME  |
|   I32   |      I64      |      2^32      |  24.170 ms |       0.58% |  24.165 ms |       0.55% |  -4.177 us |  -0.02% |  🔵 SAME  |
|   I64   |      I32      |      2^16      |  11.882 us |       4.33% |  11.913 us |       4.28% |   0.031 us |   0.26% |  🔵 SAME  |
|   I64   |      I32      |      2^20      |  24.130 us |       8.51% |  24.406 us |      11.99% |   0.276 us |   1.14% |  🔵 SAME  |
|   I64   |      I32      |      2^24      | 190.874 us |       1.38% | 190.979 us |       1.43% |   0.106 us |   0.06% |  🔵 SAME  |
|   I64   |      I32      |      2^28      |   2.795 ms |       1.22% |   2.794 ms |       1.23% |  -0.981 us |  -0.04% |  🔵 SAME  |
|   I64   |      I64      |      2^16      |  11.835 us |       4.41% |  11.824 us |       4.52% |  -0.011 us |  -0.09% |  🔵 SAME  |
|   I64   |      I64      |      2^20      |  24.362 us |      10.68% |  23.795 us |       3.85% |  -0.568 us |  -2.33% |  🔵 SAME  |
|   I64   |      I64      |      2^24      | 188.281 us |       1.86% | 187.242 us |       1.68% |  -1.040 us |  -0.55% |  🔵 SAME  |
|   I64   |      I64      |      2^28      |   2.751 ms |       0.60% |   2.749 ms |       0.66% |  -1.744 us |  -0.06% |  🔵 SAME  |
|   I64   |      I64      |      2^32      |  44.103 ms |       0.13% |  44.065 ms |       0.11% | -37.969 us |  -0.09% |  🔵 SAME  |
|  I128   |      I32      |      2^16      |  19.217 us |       2.48% |  19.116 us |       2.74% |  -0.102 us |  -0.53% |  🔵 SAME  |
|  I128   |      I32      |      2^20      |  58.094 us |       1.66% |  58.391 us |       1.49% |   0.297 us |   0.51% |  🔵 SAME  |
|  I128   |      I32      |      2^24      | 641.576 us |       0.18% | 642.476 us |       0.18% |   0.899 us |   0.14% |  🔵 SAME  |
|  I128   |      I32      |      2^28      |   9.935 ms |       0.06% |   9.941 ms |       0.06% |   6.121 us |   0.06% |  🔴 SLOW  |
|  I128   |      I64      |      2^16      |  19.036 us |       2.69% |  19.025 us |       2.77% |  -0.010 us |  -0.05% |  🔵 SAME  |
|  I128   |      I64      |      2^20      |  58.401 us |       1.78% |  58.068 us |       1.73% |  -0.333 us |  -0.57% |  🔵 SAME  |
|  I128   |      I64      |      2^24      | 641.341 us |       0.19% | 639.172 us |       0.25% |  -2.169 us |  -0.34% |  🟢 FAST  |
|  I128   |      I64      |      2^28      |   9.938 ms |       0.06% |   9.917 ms |       0.09% | -21.314 us |  -0.21% |  🟢 FAST  |
|   F32   |      I32      |      2^16      |  10.900 us |       4.57% |  10.981 us |       4.48% |   0.081 us |   0.74% |  🔵 SAME  |
|   F32   |      I32      |      2^20      |  18.790 us |       3.77% |  18.611 us |       3.45% |  -0.179 us |  -0.95% |  🔵 SAME  |
|   F32   |      I32      |      2^24      | 110.930 us |       1.73% | 110.811 us |       1.79% |  -0.118 us |  -0.11% |  🔵 SAME  |
|   F32   |      I32      |      2^28      |   1.604 ms |       0.33% |   1.602 ms |       0.36% |  -2.248 us |  -0.14% |  🔵 SAME  |
|   F32   |      I64      |      2^16      |  10.971 us |       4.44% |  10.945 us |       4.64% |  -0.027 us |  -0.24% |  🔵 SAME  |
|   F32   |      I64      |      2^20      |  18.073 us |       3.21% |  18.244 us |       3.03% |   0.171 us |   0.95% |  🔵 SAME  |
|   F32   |      I64      |      2^24      | 111.127 us |       1.84% | 110.716 us |       1.81% |  -0.411 us |  -0.37% |  🔵 SAME  |
|   F32   |      I64      |      2^28      |   1.626 ms |       0.38% |   1.623 ms |       0.37% |  -2.993 us |  -0.18% |  🔵 SAME  |
|   F32   |      I64      |      2^32      |  25.467 ms |       0.50% |  25.416 ms |       0.46% | -50.732 us |  -0.20% |  🔵 SAME  |
|   F64   |      I32      |      2^16      |  11.756 us |       4.42% |  11.725 us |       4.35% |  -0.031 us |  -0.26% |  🔵 SAME  |
|   F64   |      I32      |      2^20      |  26.534 us |      13.72% |  27.066 us |      17.79% |   0.533 us |   2.01% |  🔵 SAME  |
|   F64   |      I32      |      2^24      | 196.332 us |       1.35% | 196.381 us |       1.34% |   0.049 us |   0.02% |  🔵 SAME  |
|   F64   |      I32      |      2^28      |   2.878 ms |       1.04% |   2.879 ms |       1.03% |   1.535 us |   0.05% |  🔵 SAME  |
|   F64   |      I64      |      2^16      |  11.522 us |       3.86% |  11.615 us |       4.31% |   0.094 us |   0.81% |  🔵 SAME  |
|   F64   |      I64      |      2^20      |  28.023 us |      21.94% |  29.263 us |      25.30% |   1.240 us |   4.42% |  🔵 SAME  |
|   F64   |      I64      |      2^24      | 193.241 us |       1.51% | 193.497 us |       1.65% |   0.256 us |   0.13% |  🔵 SAME  |
|   F64   |      I64      |      2^28      |   2.860 ms |       0.51% |   2.861 ms |       0.47% |   0.643 us |   0.02% |  🔵 SAME  |
|   F64   |      I64      |      2^32      |  45.844 ms |       0.06% |  45.864 ms |       0.06% |  20.060 us |   0.04% |  🔵 SAME  |
|   C32   |      I32      |      2^16      |  11.401 us |       3.99% |  11.317 us |       3.33% |  -0.084 us |  -0.74% |  🔵 SAME  |
|   C32   |      I32      |      2^20      |  23.996 us |       2.28% |  24.020 us |       2.24% |   0.025 us |   0.10% |  🔵 SAME  |
|   C32   |      I32      |      2^24      | 196.572 us |       1.27% | 196.460 us |       1.31% |  -0.113 us |  -0.06% |  🔵 SAME  |
|   C32   |      I32      |      2^28      |   2.968 ms |       0.34% |   2.966 ms |       0.32% |  -1.606 us |  -0.05% |  🔵 SAME  |
|   C32   |      I64      |      2^16      |  11.579 us |       4.14% |  11.584 us |       4.14% |   0.004 us |   0.04% |  🔵 SAME  |
|   C32   |      I64      |      2^20      |  24.047 us |       2.27% |  24.180 us |       2.20% |   0.132 us |   0.55% |  🔵 SAME  |
|   C32   |      I64      |      2^24      | 197.551 us |       1.32% | 197.549 us |       1.33% |  -0.003 us |  -0.00% |  🔵 SAME  |
|   C32   |      I64      |      2^28      |   2.936 ms |       0.76% |   2.924 ms |       0.52% | -11.454 us |  -0.39% |  🔵 SAME  |
|   C32   |      I64      |      2^32      |  46.664 ms |       0.07% |  46.649 ms |       0.08% | -14.961 us |  -0.03% |  🔵 SAME  |

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🟥 Finished in 2h 30m: Pass: 99%/287 | Total: 12d 06h | Max: 2h 29m | Hits: 19%/1025041

See results here.

@gonidelis

gonidelis commented Jul 14, 2026

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this pr against main does not regress on b200

(cccl) ggonidelis@umb-b200-261:/src/cccl-pr9854-base/build$ python3 /src/cccl-34x/build/_deps/nvbench-src/python/scripts/nvbench_compare.py --no-color   /src/ses_9854base.json /src/ses_9854.json
['/src/ses_9854base.json', '/src/ses_9854.json']
# base

## [0] NVIDIA B200

|  T{ct}  |  OffsetT{ct}  |  Elements{io}  |   Ref Time |   Ref Noise |   Cmp Time |   Cmp Noise |       Diff |   %Diff |  Status  |
|---------|---------------|----------------|------------|-------------|------------|-------------|------------|---------|----------|
|   I8    |      I32      |      2^16      |  11.254 us |       0.45% |  11.261 us |       0.46% |   0.007 us |   0.07% |  🔵 SAME  |
|   I8    |      I32      |      2^20      |  12.593 us |       7.73% |  12.723 us |       7.15% |   0.130 us |   1.03% |  🔵 SAME  |
|   I8    |      I32      |      2^24      |  27.947 us |       2.63% |  27.908 us |       2.49% |  -0.039 us |  -0.14% |  🔵 SAME  |
|   I8    |      I32      |      2^28      | 209.738 us |       0.51% | 209.899 us |       0.47% |   0.161 us |   0.08% |  🔵 SAME  |
|   I8    |      I64      |      2^16      |  11.262 us |       0.43% |  11.262 us |       0.50% |  -0.001 us |  -0.01% |  🔵 SAME  |
|   I8    |      I64      |      2^20      |  13.210 us |       2.91% |  13.224 us |       2.83% |   0.014 us |   0.11% |  🔵 SAME  |
|   I8    |      I64      |      2^24      |  28.029 us |       2.87% |  27.888 us |       2.47% |  -0.141 us |  -0.50% |  🔵 SAME  |
|   I8    |      I64      |      2^28      | 211.224 us |       0.47% | 211.048 us |       0.49% |  -0.176 us |  -0.08% |  🔵 SAME  |
|   I8    |      I64      |      2^32      |   3.175 ms |       0.27% |   3.173 ms |       0.06% |  -1.119 us |  -0.04% |  🔵 SAME  |
|   I16   |      I32      |      2^16      |  11.265 us |       0.54% |  11.259 us |       0.49% |  -0.006 us |  -0.05% |  🔵 SAME  |
|   I16   |      I32      |      2^20      |  13.232 us |       2.81% |  13.251 us |       2.38% |   0.019 us |   0.14% |  🔵 SAME  |
|   I16   |      I32      |      2^24      |  28.230 us |       3.70% |  28.385 us |       3.75% |   0.155 us |   0.55% |  🔵 SAME  |
|   I16   |      I32      |      2^28      | 213.127 us |       0.56% | 213.061 us |       0.54% |  -0.066 us |  -0.03% |  🔵 SAME  |
|   I16   |      I64      |      2^16      |  11.261 us |       0.64% |  11.259 us |       0.47% |  -0.002 us |  -0.02% |  🔵 SAME  |
|   I16   |      I64      |      2^20      |  12.986 us |       5.73% |  12.938 us |       6.06% |  -0.048 us |  -0.37% |  🔵 SAME  |
|   I16   |      I64      |      2^24      |  29.972 us |       3.76% |  30.011 us |       3.50% |   0.039 us |   0.13% |  🔵 SAME  |
|   I16   |      I64      |      2^28      | 211.505 us |       0.62% | 211.674 us |       0.61% |   0.169 us |   0.08% |  🔵 SAME  |
|   I16   |      I64      |      2^32      |   3.249 ms |       1.51% |   3.285 ms |       1.47% |  35.835 us |   1.10% |  🔵 SAME  |
|   I32   |      I32      |      2^16      |   9.832 us |       9.53% |   9.656 us |       8.77% |  -0.176 us |  -1.79% |  🔵 SAME  |
|   I32   |      I32      |      2^20      |  13.182 us |       4.04% |  13.152 us |       4.54% |  -0.030 us |  -0.23% |  🔵 SAME  |
|   I32   |      I32      |      2^24      |  35.789 us |       3.24% |  35.818 us |       3.30% |   0.028 us |   0.08% |  🔵 SAME  |
|   I32   |      I32      |      2^28      | 322.907 us |       0.50% | 322.808 us |       0.55% |  -0.099 us |  -0.03% |  🔵 SAME  |
|   I32   |      I64      |      2^16      |   9.723 us |       9.06% |   9.660 us |       8.86% |  -0.063 us |  -0.65% |  🔵 SAME  |
|   I32   |      I64      |      2^20      |  12.948 us |       6.10% |  12.949 us |       6.69% |   0.001 us |   0.01% |  🔵 SAME  |
|   I32   |      I64      |      2^24      |  35.871 us |       3.19% |  35.910 us |       3.18% |   0.039 us |   0.11% |  🔵 SAME  |
|   I32   |      I64      |      2^28      | 322.872 us |       0.55% | 322.683 us |       0.50% |  -0.188 us |  -0.06% |  🔵 SAME  |
|   I32   |      I64      |      2^32      |   4.994 ms |       0.92% |   5.038 ms |       1.15% |  43.860 us |   0.88% |  🔵 SAME  |
|   I64   |      I32      |      2^16      |  11.266 us |       1.19% |  11.266 us |       0.95% |   0.000 us |   0.00% |  🔵 SAME  |
|   I64   |      I32      |      2^20      |  15.943 us |       5.87% |  16.027 us |       6.08% |   0.084 us |   0.53% |  🔵 SAME  |
|   I64   |      I32      |      2^24      |  54.290 us |       1.80% |  54.602 us |       1.81% |   0.311 us |   0.57% |  🔵 SAME  |
|   I64   |      I32      |      2^28      | 625.374 us |       0.29% | 625.037 us |       0.28% |  -0.338 us |  -0.05% |  🔵 SAME  |
|   I64   |      I64      |      2^16      |  11.262 us |       0.51% |  11.257 us |       0.55% |  -0.005 us |  -0.04% |  🔵 SAME  |
|   I64   |      I64      |      2^20      |  15.484 us |       3.38% |  15.489 us |       3.34% |   0.005 us |   0.03% |  🔵 SAME  |
|   I64   |      I64      |      2^24      |  54.337 us |       1.80% |  54.409 us |       1.80% |   0.072 us |   0.13% |  🔵 SAME  |
|   I64   |      I64      |      2^28      | 625.582 us |       0.28% | 625.186 us |       0.27% |  -0.396 us |  -0.06% |  🔵 SAME  |
|   I64   |      I64      |      2^32      |  10.251 ms |       0.95% |  10.338 ms |       0.78% |  87.303 us |   0.85% |  🔴 SLOW  |
|  I128   |      I32      |      2^16      |  12.610 us |       7.71% |  12.168 us |       8.35% |  -0.442 us |  -3.51% |  🔵 SAME  |
|  I128   |      I32      |      2^20      |  21.542 us |       1.51% |  21.545 us |       1.55% |   0.002 us |   0.01% |  🔵 SAME  |
|  I128   |      I32      |      2^24      | 149.502 us |       0.80% | 149.664 us |       0.77% |   0.161 us |   0.11% |  🔵 SAME  |
|  I128   |      I32      |      2^28      |   2.062 ms |       0.15% |   2.072 ms |       0.14% |  10.677 us |   0.52% |  🔴 SLOW  |
|  I128   |      I64      |      2^16      |  13.178 us |       3.82% |  13.176 us |       3.97% |  -0.002 us |  -0.01% |  🔵 SAME  |
|  I128   |      I64      |      2^20      |  23.254 us |       3.59% |  23.460 us |       2.59% |   0.207 us |   0.89% |  🔵 SAME  |
|  I128   |      I64      |      2^24      | 150.372 us |       0.77% | 150.916 us |       0.80% |   0.545 us |   0.36% |  🔵 SAME  |
|  I128   |      I64      |      2^28      |   2.062 ms |       0.15% |   2.073 ms |       0.14% |  10.965 us |   0.53% |  🔴 SLOW  |
|  I128   |      I64      |      2^32      |  32.600 ms |       0.03% |  32.783 ms |       0.03% | 183.795 us |   0.56% |  🔴 SLOW  |
|   F32   |      I32      |      2^16      |  10.777 us |       8.02% |  10.559 us |       9.13% |  -0.218 us |  -2.03% |  🔵 SAME  |
|   F32   |      I32      |      2^20      |  13.365 us |       3.08% |  13.359 us |       3.52% |  -0.006 us |  -0.04% |  🔵 SAME  |
|   F32   |      I32      |      2^24      |  36.520 us |       2.91% |  36.730 us |       3.02% |   0.210 us |   0.58% |  🔵 SAME  |
|   F32   |      I32      |      2^28      | 320.841 us |       0.43% | 320.978 us |       0.42% |   0.137 us |   0.04% |  🔵 SAME  |
|   F32   |      I64      |      2^16      |  10.567 us |       9.24% |  10.574 us |       9.15% |   0.007 us |   0.07% |  🔵 SAME  |
|   F32   |      I64      |      2^20      |  13.487 us |       4.89% |  13.461 us |       5.17% |  -0.026 us |  -0.19% |  🔵 SAME  |
|   F32   |      I64      |      2^24      |  36.735 us |       3.03% |  36.710 us |       3.09% |  -0.024 us |  -0.07% |  🔵 SAME  |
|   F32   |      I64      |      2^28      | 321.054 us |       0.51% | 321.093 us |       0.49% |   0.038 us |   0.01% |  🔵 SAME  |
|   F32   |      I64      |      2^32      |   4.865 ms |       0.67% |   4.860 ms |       0.63% |  -4.601 us |  -0.09% |  🔵 SAME  |
|   F64   |      I32      |      2^16      |  11.275 us |       1.87% |  11.282 us |       2.30% |   0.007 us |   0.06% |  🔵 SAME  |
|   F64   |      I32      |      2^20      |  16.383 us |       6.27% |  16.265 us |       6.30% |  -0.118 us |  -0.72% |  🔵 SAME  |
|   F64   |      I32      |      2^24      |  56.907 us |       1.98% |  56.826 us |       1.92% |  -0.081 us |  -0.14% |  🔵 SAME  |
|   F64   |      I32      |      2^28      | 623.181 us |       0.25% | 623.058 us |       0.25% |  -0.123 us |  -0.02% |  🔵 SAME  |
|   F64   |      I64      |      2^16      |  11.257 us |       0.48% |  11.257 us |       0.57% |  -0.000 us |  -0.00% |  🔵 SAME  |
|   F64   |      I64      |      2^20      |  16.859 us |       5.40% |  16.675 us |       5.85% |  -0.183 us |  -1.09% |  🔵 SAME  |
|   F64   |      I64      |      2^24      |  56.930 us |       1.97% |  56.748 us |       1.97% |  -0.182 us |  -0.32% |  🔵 SAME  |
|   F64   |      I64      |      2^28      | 623.043 us |       0.23% | 623.061 us |       0.25% |   0.018 us |   0.00% |  🔵 SAME  |
|   F64   |      I64      |      2^32      |   9.784 ms |       0.47% |   9.842 ms |       0.58% |  57.384 us |   0.59% |  🔴 SLOW  |
|   C32   |      I32      |      2^16      |  11.305 us |       2.64% |  11.313 us |       3.03% |   0.007 us |   0.07% |  🔵 SAME  |
|   C32   |      I32      |      2^20      |  15.994 us |       6.00% |  15.860 us |       5.63% |  -0.134 us |  -0.84% |  🔵 SAME  |
|   C32   |      I32      |      2^24      |  55.027 us |       2.06% |  54.961 us |       2.03% |  -0.067 us |  -0.12% |  🔵 SAME  |
|   C32   |      I32      |      2^28      | 622.923 us |       0.22% | 622.674 us |       0.23% |  -0.249 us |  -0.04% |  🔵 SAME  |
|   C32   |      I64      |      2^16      |  11.257 us |       0.48% |  11.261 us |       0.49% |   0.004 us |   0.04% |  🔵 SAME  |
|   C32   |      I64      |      2^20      |  15.760 us |       5.28% |  15.676 us |       4.77% |  -0.084 us |  -0.53% |  🔵 SAME  |
|   C32   |      I64      |      2^24      |  54.998 us |       2.13% |  54.849 us |       1.86% |  -0.149 us |  -0.27% |  🔵 SAME  |
|   C32   |      I64      |      2^28      | 623.031 us |       0.24% | 622.876 us |       0.22% |  -0.155 us |  -0.02% |  🔵 SAME  |
|   C32   |      I64      |      2^32      |   9.709 ms |       0.04% |   9.708 ms |       0.03% |  -1.453 us |  -0.01% |  🔵 SAME  |
|   F16   |      I32      |      2^16      |  11.271 us |       1.61% |  11.268 us |       1.55% |  -0.003 us |  -0.02% |  🔵 SAME  |
|   F16   |      I32      |      2^20      |  13.254 us |       2.28% |  13.311 us |       1.94% |   0.056 us |   0.43% |  🔵 SAME  |
|   F16   |      I32      |      2^24      |  29.116 us |       3.65% |  29.015 us |       3.91% |  -0.101 us |  -0.35% |  🔵 SAME  |
|   F16   |      I32      |      2^28      | 225.664 us |       0.53% | 225.652 us |       0.52% |  -0.012 us |  -0.01% |  🔵 SAME  |
|   F16   |      I64      |      2^16      |  11.260 us |       0.53% |  11.255 us |       0.53% |  -0.005 us |  -0.05% |  🔵 SAME  |
|   F16   |      I64      |      2^20      |  13.304 us |       1.74% |  13.320 us |       1.45% |   0.017 us |   0.12% |  🔵 SAME  |
|   F16   |      I64      |      2^24      |  29.262 us |       3.71% |  29.194 us |       3.76% |  -0.067 us |  -0.23% |  🔵 SAME  |
|   F16   |      I64      |      2^28      | 225.751 us |       0.52% | 225.709 us |       0.52% |  -0.042 us |  -0.02% |  🔵 SAME  |
|   F16   |      I64      |      2^32      |   3.338 ms |       0.70% |   3.339 ms |       0.71% |   0.699 us |   0.02% |  🔵 SAME  |
|  BF16   |      I32      |      2^16      |  11.261 us |       0.64% |  11.259 us |       0.55% |  -0.002 us |  -0.02% |  🔵 SAME  |
|  BF16   |      I32      |      2^20      |  13.292 us |       1.05% |  13.305 us |       2.17% |   0.012 us |   0.09% |  🔵 SAME  |
|  BF16   |      I32      |      2^24      |  29.141 us |       3.74% |  29.186 us |       3.87% |   0.045 us |   0.15% |  🔵 SAME  |
|  BF16   |      I32      |      2^28      | 225.623 us |       0.52% | 225.722 us |       0.50% |   0.100 us |   0.04% |  🔵 SAME  |
|  BF16   |      I64      |      2^16      |  11.259 us |       0.69% |  11.258 us |       0.51% |  -0.000 us |  -0.00% |  🔵 SAME  |
|  BF16   |      I64      |      2^20      |  13.269 us |       2.31% |  13.290 us |       1.94% |   0.021 us |   0.16% |  🔵 SAME  |
|  BF16   |      I64      |      2^24      |  29.213 us |       3.62% |  29.043 us |       3.69% |  -0.170 us |  -0.58% |  🔵 SAME  |
|  BF16   |      I64      |      2^28      | 225.783 us |       0.51% | 225.584 us |       0.54% |  -0.199 us |  -0.09% |  🔵 SAME  |
|  BF16   |      I64      |      2^32      |   3.338 ms |       0.80% |   3.338 ms |       0.66% |  -0.135 us |  -0.00% |  🔵 SAME  |

# Summary

- Total Matches: 90
  - Pass    (diff <= min_noise): 85
  - Unknown (infinite noise):    0
  - Failure (diff > min_noise):  5

@coderabbitai coderabbitai Bot mentioned this pull request Jul 14, 2026
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@bernhardmgruber

bernhardmgruber commented Jul 14, 2026

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Closed in favor of: #9858

@github-project-automation github-project-automation Bot moved this from In Review to Done in CCCL Jul 14, 2026
@bernhardmgruber
bernhardmgruber deleted the fix_scan_reg branch July 14, 2026 16:39
@gevtushenko gevtushenko mentioned this pull request Sep 7, 2026
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@pauleonix pauleonix pauleonix approved these changes
@davebayer davebayer davebayer approved these changes
@srinivasyadav18 srinivasyadav18 Awaiting requested review from srinivasyadav18 srinivasyadav18 is a code owner automatically assigned from NVIDIA/cccl-cub-codeowners

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backport branch/3.4.x

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scan_exclusive_sum regresses in CCCL 3.4 on Ampere

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@bernhardmgruber @elstehle @gonidelis @pauleonix @davebayer