Remove _CCCL_GRID_CONSTANT from merge sort kernel parameters by nanan-nvidia · Pull Request #9829 · NVIDIA/cccl

nanan-nvidia · 2026-07-13T19:36:51Z

This fixes observed regressions on merge_sort_keys and merge_sort_pairs

merge_sort_keys, B200

| T    | OffsetT | Elements | Entropy | 3.3.4 | 3.4.0 | 3.4.0-noGC | 3.4.0 vs 3.3.4 | 3.4.0-noGC vs 3.3.4 |
|------|---------|----------|---------|-------|-------|------------|----------------|---------------------|
| I8   | I32     |     2^24 |   1.000 | 0.71% | 0.70% |      0.71% |  -2.31% 🔴 SLOW |       -0.01% 🔵 SAME |
| I8   | I32     |     2^24 |   0.201 | 0.76% | 0.74% |      0.76% |  -2.14% 🔴 SLOW |       -0.01% 🔵 SAME |
| I8   | I32     |     2^28 |   1.000 | 0.72% | 0.69% |      0.72% |  -3.58% 🔴 SLOW |       -0.01% 🔵 SAME |
| I8   | I32     |     2^28 |   0.201 | 0.76% | 0.74% |      0.76% |  -3.54% 🔴 SLOW |       +0.01% 🔵 SAME |
| I8   | I64     |     2^24 |   1.000 | 0.70% | 0.68% |      0.70% |  -2.16% 🔴 SLOW |       -0.00% 🔵 SAME |
| I8   | I64     |     2^24 |   0.201 | 0.74% | 0.72% |      0.74% |  -2.14% 🔴 SLOW |       +0.00% 🔵 SAME |
| I8   | I64     |     2^28 |   1.000 | 0.70% | 0.68% |      0.70% |  -3.38% 🔴 SLOW |       +0.01% 🔵 SAME |
| I8   | I64     |     2^28 |   0.201 | 0.75% | 0.72% |      0.75% |  -3.84% 🔴 SLOW |       +0.01% 🔵 SAME |
| I16  | I32     |     2^24 |   1.000 | 1.36% | 1.31% |      1.36% |  -3.66% 🔴 SLOW |       -0.01% 🔵 SAME |
| I16  | I32     |     2^24 |   0.201 | 1.47% | 1.42% |      1.48% |  -3.93% 🔴 SLOW |       +0.28% 🟢 FAST |
| I16  | I32     |     2^28 |   1.000 | 1.33% | 1.25% |      1.33% |  -6.62% 🔴 SLOW |       -0.02% 🔵 SAME |
| I16  | I32     |     2^28 |   0.201 | 1.52% | 1.41% |      1.52% |  -7.65% 🔴 SLOW |       -0.02% 🔵 SAME |
| I16  | I64     |     2^24 |   1.000 | 1.33% | 1.28% |      1.33% |  -3.58% 🔴 SLOW |       +0.02% 🔵 SAME |
| I16  | I64     |     2^24 |   0.201 | 1.42% | 1.39% |      1.42% |  -2.08% 🔴 SLOW |       +0.21% 🟢 FAST |
| I16  | I64     |     2^28 |   1.000 | 1.29% | 1.22% |      1.29% |  -5.67% 🔴 SLOW |       -0.03% 🔵 SAME |
| I16  | I64     |     2^28 |   0.201 | 1.45% | 1.38% |      1.45% |  -4.64% 🔴 SLOW |       -0.03% 🔵 SAME |
| I32  | I32     |     2^24 |   1.000 | 2.58% | 2.42% |      2.58% |  -6.11% 🔴 SLOW |       -0.09% 🔵 SAME |
| I32  | I32     |     2^24 |   0.201 | 2.86% | 2.65% |      2.86% |  -7.34% 🔴 SLOW |       -0.11% 🔵 SAME |
| I32  | I32     |     2^28 |   1.000 | 2.77% | 2.63% |      2.77% |  -5.27% 🔴 SLOW |       -0.01% 🔵 SAME |
| I32  | I32     |     2^28 |   0.201 | 3.23% | 2.96% |      3.23% |  -8.45% 🔴 SLOW |       +0.03% 🔵 SAME |
| I32  | I64     |     2^24 |   1.000 | 2.56% | 2.42% |      2.56% |  -5.45% 🔴 SLOW |       +0.09% 🔵 SAME |
| I32  | I64     |     2^24 |   0.201 | 2.76% | 2.62% |      2.75% |  -4.97% 🔴 SLOW |       -0.18% 🔴 SLOW |
| I32  | I64     |     2^28 |   1.000 | 2.72% | 2.59% |      2.72% |  -4.76% 🔴 SLOW |       +0.01% 🔵 SAME |
| I32  | I64     |     2^28 |   0.201 | 3.07% | 2.91% |      3.07% |  -5.26% 🔴 SLOW |       +0.02% 🔵 SAME |
| I64  | I32     |     2^24 |   1.000 | 2.39% | 2.37% |      2.39% |  -1.06% 🔴 SLOW |       +0.04% 🔵 SAME |
| I64  | I32     |     2^24 |   0.201 | 2.27% | 2.24% |      2.27% |  -1.26% 🔴 SLOW |       -0.03% 🔵 SAME |
| I64  | I32     |     2^28 |   1.000 | 2.26% | 2.21% |      2.26% |  -2.09% 🔴 SLOW |       -0.02% 🔵 SAME |
| I64  | I32     |     2^28 |   0.201 | 2.14% | 2.10% |      2.13% |  -1.77% 🔴 SLOW |       -0.02% 🔵 SAME |
| I64  | I64     |     2^24 |   1.000 | 2.39% | 2.36% |      2.39% |  -1.47% 🔴 SLOW |       -0.04% 🔵 SAME |
| I64  | I64     |     2^24 |   0.201 | 2.26% | 2.23% |      2.26% |  -1.33% 🔴 SLOW |       -0.04% 🔵 SAME |
| I64  | I64     |     2^28 |   1.000 | 2.25% | 2.20% |      2.25% |  -1.94% 🔴 SLOW |       +0.03% 🔵 SAME |
| I64  | I64     |     2^28 |   0.201 | 2.13% | 2.09% |      2.13% |  -1.78% 🔴 SLOW |       +0.02% 🔵 SAME |
| I128 | I32     |     2^24 |   1.000 | 2.25% | 2.17% |      2.24% |  -3.35% 🔴 SLOW |       -0.08% 🔵 SAME |
| I128 | I32     |     2^24 |   0.201 | 2.31% | 2.27% |      2.31% |  -1.72% 🔴 SLOW |       -0.01% 🔵 SAME |
| I128 | I32     |     2^28 |   1.000 | 1.97% | 1.92% |      1.97% |  -2.51% 🔴 SLOW |       -0.01% 🔵 SAME |
| I128 | I32     |     2^28 |   0.201 | 2.09% | 2.05% |      2.09% |  -1.70% 🔴 SLOW |       -0.01% 🔵 SAME |
| I128 | I64     |     2^24 |   1.000 | 2.24% | 2.23% |      2.24% |  -0.27% 🔴 SLOW |       -0.06% 🔵 SAME |
| I128 | I64     |     2^24 |   0.201 | 2.30% | 2.30% |      2.30% |  -0.00% 🔵 SAME |       -0.04% 🔵 SAME |
| I128 | I64     |     2^28 |   1.000 | 1.96% | 1.95% |      1.96% |  -0.57% 🔴 SLOW |       -0.01% 🔴 SLOW |
| I128 | I64     |     2^28 |   0.201 | 2.08% | 2.07% |      2.08% |  -0.09% 🔴 SLOW |       -0.00% 🔵 SAME |
| F32  | I32     |     2^24 |   1.000 | 2.58% | 2.42% |      2.58% |  -6.08% 🔴 SLOW |       +0.11% 🔵 SAME |
| F32  | I32     |     2^24 |   0.201 | 2.85% | 2.64% |      2.85% |  -7.44% 🔴 SLOW |       -0.04% 🔵 SAME |
| F32  | I32     |     2^28 |   1.000 | 2.77% | 2.63% |      2.77% |  -5.25% 🔴 SLOW |       +0.05% 🔵 SAME |
| F32  | I32     |     2^28 |   0.201 | 3.23% | 2.96% |      3.23% |  -8.39% 🔴 SLOW |       +0.02% 🔵 SAME |
| F32  | I64     |     2^24 |   1.000 | 2.56% | 2.41% |      2.56% |  -5.70% 🔴 SLOW |       -0.03% 🔵 SAME |
| F32  | I64     |     2^24 |   0.201 | 2.75% | 2.61% |      2.75% |  -4.92% 🔴 SLOW |       -0.01% 🔵 SAME |
| F32  | I64     |     2^28 |   1.000 | 2.72% | 2.59% |      2.72% |  -4.83% 🔴 SLOW |       -0.01% 🔵 SAME |
| F32  | I64     |     2^28 |   0.201 | 3.07% | 2.91% |      3.07% |  -5.17% 🔴 SLOW |       +0.02% 🔵 SAME |
| F64  | I32     |     2^24 |   1.000 | 2.40% | 2.36% |      2.39% |  -1.63% 🔴 SLOW |       -0.48% 🔴 SLOW |
| F64  | I32     |     2^24 |   0.201 | 2.30% | 2.27% |      2.29% |  -1.19% 🔴 SLOW |       -0.03% 🔵 SAME |
| F64  | I32     |     2^28 |   1.000 | 2.27% | 2.22% |      2.27% |  -1.99% 🔴 SLOW |       +0.02% 🔵 SAME |
| F64  | I32     |     2^28 |   0.201 | 2.14% | 2.11% |      2.14% |  -1.76% 🔴 SLOW |       +0.02% 🔵 SAME |
| F64  | I64     |     2^24 |   1.000 | 2.40% | 2.36% |      2.38% |  -1.74% 🔴 SLOW |       -0.75% 🔴 SLOW |
| F64  | I64     |     2^24 |   0.201 | 2.29% | 2.26% |      2.29% |  -1.20% 🔴 SLOW |       +0.06% 🔵 SAME |
| F64  | I64     |     2^28 |   1.000 | 2.26% | 2.21% |      2.26% |  -1.96% 🔴 SLOW |       +0.01% 🔵 SAME |
| F64  | I64     |     2^28 |   0.201 | 2.14% | 2.10% |      2.14% |  -1.86% 🔴 SLOW |       -0.02% 🔵 SAME |
| C32  | I32     |     2^24 |   1.000 | 0.80% | 0.80% |      0.80% |  +0.10% 🔵 SAME |       -0.00% 🔵 SAME |
| C32  | I32     |     2^24 |   0.201 | 0.55% | 0.55% |      0.55% |  -0.32% 🔴 SLOW |       +0.03% 🔵 SAME |
| C32  | I32     |     2^28 |   1.000 | 0.68% | 0.68% |      0.68% |  +0.12% 🟢 FAST |       -0.00% 🔵 SAME |
| C32  | I32     |     2^28 |   0.201 | 0.54% | 0.54% |      0.54% |  -0.34% 🔴 SLOW |       +0.00% 🔵 SAME |
| C32  | I64     |     2^24 |   1.000 | 0.81% | 0.81% |      0.81% |  -0.42% 🔴 SLOW |       -0.03% 🔵 SAME |
| C32  | I64     |     2^24 |   0.201 | 0.55% | 0.55% |      0.55% |  +0.26% 🟢 FAST |       -0.00% 🔵 SAME |
| C32  | I64     |     2^28 |   1.000 | 0.69% | 0.69% |      0.69% |  -0.47% 🔴 SLOW |       +0.00% 🔵 SAME |
| C32  | I64     |     2^28 |   0.201 | 0.54% | 0.54% |      0.54% |  +0.19% 🟢 FAST |       -0.00% 🔵 SAME |

merge_sort_pairs, B200

| KeyT | ValueT | OffsetT | Elements | Entropy | 3.3.4 | 3.4.0 | 3.4.0-noGC | 3.4.0 vs 3.3.4 | 3.4.0-noGC vs 3.3.4 |
|------|--------|---------|----------|---------|-------|-------|------------|----------------|---------------------|
| I8   | I32    | I32     |     2^24 |   1.000 | 1.99% | 1.87% |      1.99% |  -5.94% 🔴 SLOW |       -0.05% 🔵 SAME |
| I8   | I32    | I32     |     2^24 |   0.201 | 2.14% | 2.00% |      2.14% |  -6.44% 🔴 SLOW |       -0.00% 🔵 SAME |
| I8   | I32    | I32     |     2^28 |   1.000 | 1.92% | 1.78% |      1.92% |  -7.43% 🔴 SLOW |       +0.03% 🟢 FAST |
| I8   | I32    | I32     |     2^28 |   0.201 | 2.05% | 1.89% |      2.05% |  -8.13% 🔴 SLOW |       +0.04% 🟢 FAST |
| I8   | I64    | I32     |     2^24 |   1.000 | 2.61% | 2.47% |      2.61% |  -5.09% 🔴 SLOW |       +0.05% 🔵 SAME |
| I8   | I64    | I32     |     2^24 |   0.201 | 2.81% | 2.62% |      2.81% |  -6.80% 🔴 SLOW |       +0.02% 🔵 SAME |
| I8   | I64    | I32     |     2^28 |   1.000 | 2.40% | 2.26% |      2.40% |  -5.86% 🔴 SLOW |       -0.01% 🔵 SAME |
| I8   | I64    | I32     |     2^28 |   0.201 | 2.60% | 2.38% |      2.60% |  -8.46% 🔴 SLOW |       +0.00% 🔵 SAME |
| I32  | I32    | I32     |     2^24 |   1.000 | 3.07% | 2.87% |      3.07% |  -6.42% 🔴 SLOW |       +0.00% 🔵 SAME |
| I32  | I32    | I32     |     2^24 |   0.201 | 3.32% | 3.08% |      3.32% |  -7.23% 🔴 SLOW |       +0.11% 🔵 SAME |
| I32  | I32    | I32     |     2^28 |   1.000 | 2.88% | 2.68% |      2.88% |  -7.05% 🔴 SLOW |       +0.00% 🔵 SAME |
| I32  | I32    | I32     |     2^28 |   0.201 | 3.24% | 2.96% |      3.24% |  -8.63% 🔴 SLOW |       +0.01% 🔵 SAME |
| I32  | I64    | I32     |     2^24 |   1.000 | 3.30% | 3.15% |      3.31% |  -4.56% 🔴 SLOW |       +0.04% 🔵 SAME |
| I32  | I64    | I32     |     2^24 |   0.201 | 3.58% | 3.36% |      3.58% |  -6.25% 🔴 SLOW |       -0.06% 🔵 SAME |
| I32  | I64    | I32     |     2^28 |   1.000 | 2.98% | 2.85% |      2.98% |  -4.27% 🔴 SLOW |       -0.01% 🔵 SAME |
| I32  | I64    | I32     |     2^28 |   0.201 | 3.32% | 3.09% |      3.32% |  -7.08% 🔴 SLOW |       -0.04% 🔴 SLOW |
| I64  | I32    | I32     |     2^24 |   1.000 | 2.87% | 2.82% |      2.88% |  -1.86% 🔴 SLOW |       +0.09% 🟢 FAST |
| I64  | I32    | I32     |     2^24 |   0.201 | 2.69% | 2.63% |      2.69% |  -2.20% 🔴 SLOW |       +0.12% 🟢 FAST |
| I64  | I32    | I32     |     2^28 |   1.000 | 2.63% | 2.58% |      2.63% |  -1.88% 🔴 SLOW |       +0.00% 🔵 SAME |
| I64  | I32    | I32     |     2^28 |   0.201 | 2.45% | 2.38% |      2.45% |  -2.75% 🔴 SLOW |       +0.02% 🔵 SAME |
| I64  | I64    | I32     |     2^24 |   1.000 | 3.11% | 3.06% |      3.11% |  -1.46% 🔴 SLOW |       +0.06% 🟢 FAST |
| I64  | I64    | I32     |     2^24 |   0.201 | 2.86% | 2.81% |      2.86% |  -1.57% 🔴 SLOW |       +0.08% 🟢 FAST |
| I64  | I64    | I32     |     2^28 |   1.000 | 2.79% | 2.74% |      2.79% |  -1.57% 🔴 SLOW |       +0.01% 🔵 SAME |
| I64  | I64    | I32     |     2^28 |   0.201 | 2.54% | 2.50% |      2.54% |  -1.83% 🔴 SLOW |       +0.01% 🟢 FAST |
| F32  | I32    | I32     |     2^24 |   1.000 | 3.06% | 2.86% |      3.06% |  -6.29% 🔴 SLOW |       +0.12% 🟢 FAST |
| F32  | I32    | I32     |     2^24 |   0.201 | 3.31% | 3.07% |      3.31% |  -7.21% 🔴 SLOW |       +0.06% 🔵 SAME |
| F32  | I32    | I32     |     2^28 |   1.000 | 2.87% | 2.67% |      2.87% |  -7.00% 🔴 SLOW |       +0.02% 🔵 SAME |
| F32  | I32    | I32     |     2^28 |   0.201 | 3.23% | 2.95% |      3.23% |  -8.59% 🔴 SLOW |       +0.01% 🔵 SAME |
| F32  | I64    | I32     |     2^24 |   1.000 | 3.30% | 3.15% |      3.30% |  -4.62% 🔴 SLOW |       -0.04% 🔵 SAME |
| F32  | I64    | I32     |     2^24 |   0.201 | 3.57% | 3.36% |      3.57% |  -6.07% 🔴 SLOW |       -0.00% 🔵 SAME |
| F32  | I64    | I32     |     2^28 |   1.000 | 2.97% | 2.85% |      2.97% |  -4.23% 🔴 SLOW |       -0.03% 🔴 SLOW |
| F32  | I64    | I32     |     2^28 |   0.201 | 3.32% | 3.08% |      3.32% |  -6.97% 🔴 SLOW |       +0.04% 🟢 FAST |

copy-pr-bot · 2026-07-13T19:36:55Z

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nanan-nvidia · 2026-07-13T19:37:25Z

/ok to test 174518f

coderabbitai · 2026-07-13T19:38:48Z

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cub/cub/device/dispatch/kernels/kernel_merge_sort.cuh

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Summary by CodeRabbit

Bug Fixes
- Improved CUDA merge-sort kernel compatibility by adjusting parameter declarations.
- Preserved existing merge-sort behavior and processing logic.

Walkthrough

Changes

Merge sort kernel signatures

Layer / File(s)	Summary
Kernel parameter qualifier updates `cub/cub/device/dispatch/kernels/kernel_merge_sort.cuh`	The block-sort, partition, and merge kernel signatures replace `_CCCL_GRID_CONSTANT` parameter qualifiers with plain `const` declarations; kernel bodies remain unchanged.

Suggested reviewers: naderalawar, bernhardmgruber

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nanan-nvidia · 2026-07-13T19:52:37Z

/ok to test 3494ff9

github-actions · 2026-07-13T22:03:34Z

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github-actions · 2026-07-13T22:04:36Z

Successfully created backport PR for branch/3.4.x:

[Backport branch/3.4.x] Remove _CCCL_GRID_CONSTANT from merge sort kernel parameters #9832

…uding merge sort (#9864) * Remove most `CCCL_GRID_CONSTANT` annotations (#9858) QA reported several regressions caused by the introduction of `_CCCL_GRID_CONSTANT` in #6642. The regressions include: - #9763 - #9765 - #9766 - #9768 - #9822 The cause of the regression is probably a compiler bug, reported in NVBug 6448961. This PR mainly reverts #6642, but since a lot of time has passed, I needed to do a lot of manual editing as well. Fixes: #9768 Fixes: #9822 Fixes: #9851 (cherry picked from commit d8fd76b) * Remove _CCCL_GRID_CONSTANT from merge sort kernel parameters (#9829) Co-authored-by: Paul Grosse-Bley <pauleonix-dev@pm.me> --------- Co-authored-by: nanan-nvidia <nan@nvidia.com> Co-authored-by: Paul Grosse-Bley <pauleonix-dev@pm.me>

Remove _CCCL_GRID_CONSTANT from merge sort kernel parameters

174518f

nanan-nvidia requested a review from a team as a code owner July 13, 2026 19:36

nanan-nvidia requested a review from NaderAlAwar July 13, 2026 19:36

github-project-automation Bot moved this to Todo in CCCL Jul 13, 2026

github-project-automation Bot added this to CCCL Jul 13, 2026

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pauleonix approved these changes Jul 13, 2026

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Merge branch 'main' into merge-gc-fix

3494ff9

nanan-nvidia self-assigned this Jul 13, 2026

nanan-nvidia added the backport branch/3.4.x label Jul 13, 2026

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nanan-nvidia merged commit 3acca0b into NVIDIA:main Jul 13, 2026
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github-project-automation Bot moved this from In Review to Done in CCCL Jul 13, 2026

github-actions Bot mentioned this pull request Jul 13, 2026

[Backport branch/3.4.x] Remove _CCCL_GRID_CONSTANT from merge sort kernel parameters #9832

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This was referenced Jul 14, 2026

Remove _CCCL_GRID_CONSTANT from DeviceReduce::ReduceByKey kernels #9852

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Remove _CCCL_GRID_CONSTANT from scan kernel #9854

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This was referenced Jul 14, 2026

Remove most CCCL_GRID_CONSTANT annotations #9858

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[Backport to 3.4] Remove most _CCCL_GRID_CONSTANT annotations, including merge sort #9864

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gevtushenko mentioned this pull request Sep 7, 2026

[EPIC]: Regression-prevention skills: perf, functional, API, ABI #11244

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Remove _CCCL_GRID_CONSTANT from merge sort kernel parameters - #9829

Remove _CCCL_GRID_CONSTANT from merge sort kernel parameters#9829
nanan-nvidia merged 2 commits into
NVIDIA:mainfrom
nanan-nvidia:merge-gc-fix

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🥳 CI Workflow Results

🟩 Finished in 2h 06m: Pass: 100%/287 | Total: 5d 14h | Max: 1h 09m | Hits: 66%/390652

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