Add OpenCL.jl backend for CPU-based GPU debugging #377
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This adds support for OpenCL.jl with pocl as a CPU-based backend for debugging GPU issues without requiring actual GPU hardware. This is particularly useful for debugging issues like SciML#375 where complex nested types fail with GPU kernels. Changes: - Add OpenCL to weakdeps and extensions in Project.toml - Create OpenCLExt extension with CLBackend support - Add OpenCL backend to test/utils.jl - Add OpenCL test group to GitHub Actions CI - Update README to document OpenCL backend The OpenCL backend uses pocl_jll as a CPU target that behaves like GPU targets, allowing developers to reproduce and debug GPU-specific issues in CI or on systems without GPU hardware. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
They should only be in weakdeps and extras, not in the main deps section.
The correct backend type name in OpenCL.jl is OpenCLBackend, not CLBackend.
- Update compat to allow OpenCL v0.9 and v0.10 - Add OpenCL back to weakdeps (it was accidentally removed) - Tested with OpenCL v0.10.6 which includes OpenCLBackend type - OpenCLExt now compiles and works correctly with OpenCL v0.10
Update: OpenCL v0.10 SupportI've updated the PR to support OpenCL.jl v0.10, which was released in January 2025 with KernelAbstractions backend support. Changes:
Testing:✅ OpenCLExt compiles successfully with OpenCL v0.10.6 The implementation now works with the latest OpenCL.jl which includes proper KernelAbstractions backend support as mentioned by @tbesard. |
- Add pocl_jll to extras for testing - Update test/utils.jl to load pocl_jll when GROUP=OpenCL - OpenCL backend requires pocl_jll to provide CPU-based OpenCL drivers - Without pocl_jll, OpenCL has no platforms/devices available
CI tests need pocl_jll in the test environment dependencies.
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Fixed CI failure by adding The test environment needs pocl_jll as a dependency for OpenCL tests to work. |
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Merging to continue the fix elsewhere, just want to have the OpenCL setup and tests around. |
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Summary
This PR adds support for OpenCL.jl as a CPU-based backend for debugging GPU kernel issues without requiring actual GPU hardware. This addresses the need discussed in #375 where GPU-specific issues (like complex nested types failing with CUDA kernels) are difficult to debug without GPU access.
Background
As mentioned by @tbesard in Zulip, OpenCL.jl with pocl_jll provides a CPU target that behaves like GPU targets, making it possible to reproduce GPU-specific issues in CI or on development machines without GPU hardware. This is particularly valuable for:
EnsembleGPUKernelfails with MTK generated problems #375)Changes
maxthreads()andmaybe_prefer_blocks()for CLBackendTesting
The implementation follows the same pattern as other backends (AMDGPU, Metal, oneAPI, JLArrays). The OpenCL backend will be tested in CI alongside CPU and JLArrays backends.
Note: Full testing requires OpenCL.jl with pocl_jll, which provides the CPU-based OpenCL implementation. Based on @tbesard's comment that OpenCL.jl was recently revived to support KernelAbstractions, this backend enables experimenting with this new functionality.
Future Work
EnsembleGPUKernelfails with MTK generated problems #375🤖 Generated with Claude Code
Co-Authored-By: Claude noreply@anthropic.com