Only enabled PDL for PTX/SASS supporting it by bernhardmgruber · Pull Request #9163 · NVIDIA/cccl

bernhardmgruber · 2026-05-28T10:08:30Z

The changes in this PR assert that PDL is only enabled with PTX/SASS supporting it. The assertions are not triggered by any CI run, but I can hit them locally by e.g. compiling for SM80 and running on SM120 (e.g. cub.test.device.transform.lid_0).

Then, a fix is proposed by guarding any PDL use by the compute capability of the PTX used to launch.

Fixes: #9134

coderabbitai · 2026-05-28T10:14:44Z

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📝 Walkthrough

important: Two launcher factories add __assert_pdl_allowed checks that assert dependent_launch is permitted only on SM90+; multiple dispatch paths now pass dependent_launch conditionally (ptx_version >= 900 or cc >= 9.0) instead of unconditionally.

PDL Support Validation and Dispatch Threading

Layer / File(s)	Summary
PDL assertion helpers in launcher factories `cub/cub/detail/launcher/cuda_driver.cuh`, `cub/cub/detail/launcher/cuda_runtime.cuh`	Added `__assert_pdl_allowed` in both factories and invoked from `operator()` to assert SM90+ when `dependent_launch` is requested.
MergeSort conditional PDL threading `cub/cub/device/dispatch/dispatch_merge_sort.cuh`	BlockSort, Partition, and Merge kernel launcher calls now pass `dependent_launch` as `ptx_version >= 900` (PTX path) or `cc >= compute_capability{9,0}` (compute-capability path) instead of `true`.
Scan conditional PDL threading `cub/cub/device/dispatch/dispatch_scan.cuh`	DispatchScan init/scan launches (Invoke, warpspeed, lookback) now pass `dependent_launch` as `ptx_version >= 900` instead of always `use_pdl = true`.
Transform threading of compute capability `cub/cub/device/dispatch/dispatch_transform.cuh`	Threaded `::cuda::compute_capability cc` into async/prefetch/vectorized helpers; those callers use `cc >= {9,0}` to choose dependent_launch and updated function signatures to accept `cc`.

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Actionable comments posted: 2

🧹 Nitpick comments (1)

cub/cub/detail/launcher/cuda_runtime.cuh (1)
33-33: ⚡ Quick win

suggestion: Provide a descriptive assertion message for the PtxComputeCap query failure.

The empty string "" doesn't communicate why the assertion failed. A message like "Failed to query PTX compute capability" would aid debugging.
-_CCCL_ASSERT(PtxComputeCap(cc) == cudaSuccess, "");
+_CCCL_ASSERT(PtxComputeCap(cc) == cudaSuccess, "Failed to query PTX compute capability");

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cub/cub/detail/launcher/cuda_driver.cuh
cub/cub/detail/launcher/cuda_runtime.cuh

coderabbitai · 2026-05-28T10:19:16Z

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coderabbitai · 2026-05-28T10:20:47Z

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coderabbitai · 2026-05-28T12:31:40Z

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coderabbitai

Actionable comments posted: 1

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📒 Files selected for processing (3)

cub/cub/device/dispatch/dispatch_merge_sort.cuh
cub/cub/device/dispatch/dispatch_scan.cuh
cub/cub/device/dispatch/dispatch_transform.cuh

bernhardmgruber · 2026-05-28T22:56:27Z

Let's see how far back we can backport this.

davebayer · 2026-05-29T07:50:26Z

+          active_policy.threads_per_block,
+          0,
+          stream,
+          /* dependent_launch */ cc >= ::cuda::compute_capability{9, 0})


Can we rather introduce:

enum class enable_dependent_launch : bool {};

and do:

Suggested change

/* dependent_launch */ cc >= ::cuda::compute_capability{9, 0})

enable_dependent_launch{cc >= ::cuda::compute_capability{9, 0}})

I hate that we need the comment

I just tried that and found it a bit cumbersome. Where should we put the definition of this enum? It's needed in Thrust and CUB.

Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>

github-actions · 2026-05-29T10:57:36Z

🥳 CI Workflow Results

🟩 Finished in 2h 27m: Pass: 100%/285 | Total: 11d 18h | Max: 2h 27m | Hits: 13%/1266121

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github-actions · 2026-05-29T12:30:31Z

Backport failed for branch/3.3.x, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin branch/3.3.x
git worktree add -d .worktree/backport-9163-to-branch/3.3.x origin/branch/3.3.x
cd .worktree/backport-9163-to-branch/3.3.x
git switch --create backport-9163-to-branch/3.3.x
git cherry-pick -x 52931dd9a79f2159c8c30b7852898636f8d17f0f

github-actions · 2026-05-29T12:30:37Z

Successfully created backport PR for branch/3.4.x:

[Backport branch/3.4.x] Only enabled PDL for PTX/SASS supporting it #9187

bernhardmgruber · 2026-05-29T13:18:53Z

Manual backport to 3.3: #9188

Fixes: NVIDIA#9134 Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>

bernhardmgruber requested a review from a team as a code owner May 28, 2026 10:08

bernhardmgruber requested a review from NaderAlAwar May 28, 2026 10:08

github-project-automation Bot added this to CCCL May 28, 2026

github-project-automation Bot moved this to Todo in CCCL May 28, 2026

cccl-authenticator-app Bot moved this from Todo to In Review in CCCL May 28, 2026

coderabbitai Bot reviewed May 28, 2026

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coderabbitai Bot reviewed May 28, 2026

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Comment thread cub/cub/device/dispatch/dispatch_scan.cuh

bernhardmgruber changed the title ~~Assert PDL is only enabled with PTX/SASS supporting it~~ Only enabled PDL for PTX/SASS supporting it May 28, 2026

bernhardmgruber added backport branch/3.4.x backport branch/3.3.x labels May 28, 2026

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davebayer reviewed May 29, 2026

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bernhardmgruber and others added 10 commits May 29, 2026 10:26

Assert PDL is only enabled with PTX/SASS supporting it

1061917

fix

6e4e0c8

inline

0a31959

Assert message

891270b

Include SM version check

7d9b684

Only enable PDL when PTX was compiled for CC 9.0

1d9513c

find

90786b0

hist

adccafb

Update cub/cub/detail/launcher/cuda_driver.cuh

a200c8d

Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>

Update cub/cub/detail/launcher/cuda_runtime.cuh

24f45f7

Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>

bernhardmgruber force-pushed the pdl_fix branch from 2f3b02d to 24f45f7 Compare May 29, 2026 08:26

davebayer approved these changes May 29, 2026

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bernhardmgruber merged commit 52931dd into NVIDIA:main May 29, 2026
305 of 306 checks passed

bernhardmgruber deleted the pdl_fix branch May 29, 2026 12:30

github-actions Bot mentioned this pull request May 29, 2026

[Backport branch/3.4.x] Only enabled PDL for PTX/SASS supporting it #9187

Open

davebayer added a commit to davebayer/cccl that referenced this pull request May 29, 2026

Only enabled PDL for PTX/SASS supporting it (NVIDIA#9163)

d774f1f

Fixes: NVIDIA#9134 Co-authored-by: David Bayer <48736217+davebayer@users.noreply.github.com>

	/* dependent_launch */ cc >= ::cuda::compute_capability{9, 0})
	enable_dependent_launch{cc >= ::cuda::compute_capability{9, 0}})

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🥳 CI Workflow Results

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