Document debugging POCL compilation with POCL_DEBUG

[vchuravy]

Adds a docs page (under Extras) on debugging POCL compilation for the CPU backend (POCLBackend):

• How to enable PoCL's debug output with POCL_DEBUG=err,warn, either in the shell or via ENV["POCL_DEBUG"] before the first kernel launch.
• Other useful categories (llvm, cache, general, all) with a sample output line.
• A note on the on-disk kernel cache (~/.cache/pocl/kcache, POCL_KERNEL_CACHE=0, POCL_CACHE_DIR), since cache hits can hide the compilation messages one is looking for.

Verified against the vendored pocl_standalone_jll (debug output confirmed for both ways of setting the variable) and that the docs build renders the page and nav entry.

🤖 Generated with Claude Code

[github-actions]

Benchmark Results

Show table

	main	1bcca1a...	main / 1bcca1a...
saxpy/default/Float32/1024	0.0607 ± 0.033 ms	0.0604 ± 0.034 ms	1 ± 0.79
saxpy/default/Float32/1048576	0.483 ± 0.018 ms	0.483 ± 0.019 ms	1 ± 0.055
saxpy/default/Float32/16384	0.0535 ± 0.03 ms	0.0554 ± 0.03 ms	0.965 ± 0.75
saxpy/default/Float32/2048	0.063 ± 0.027 ms	0.0629 ± 0.027 ms	1 ± 0.62
saxpy/default/Float32/256	0.0595 ± 0.035 ms	0.056 ± 0.036 ms	1.06 ± 0.93
saxpy/default/Float32/262144	0.173 ± 0.027 ms	0.175 ± 0.027 ms	0.986 ± 0.22
saxpy/default/Float32/32768	0.0602 ± 0.03 ms	0.061 ± 0.03 ms	0.986 ± 0.7
saxpy/default/Float32/4096	0.0664 ± 0.029 ms	0.0661 ± 0.027 ms	1 ± 0.6
saxpy/default/Float32/512	0.0582 ± 0.035 ms	0.0594 ± 0.035 ms	0.981 ± 0.83
saxpy/default/Float32/64	0.0576 ± 0.035 ms	0.0585 ± 0.035 ms	0.984 ± 0.84
saxpy/default/Float32/65536	0.0775 ± 0.03 ms	0.0894 ± 0.031 ms	0.866 ± 0.45
saxpy/default/Float64/1024	0.0612 ± 0.032 ms	0.0607 ± 0.032 ms	1.01 ± 0.75
saxpy/default/Float64/1048576	0.543 ± 0.035 ms	0.535 ± 0.028 ms	1.01 ± 0.084
saxpy/default/Float64/16384	0.0628 ± 0.03 ms	0.0702 ± 0.03 ms	0.894 ± 0.58
saxpy/default/Float64/2048	0.0644 ± 0.027 ms	0.0636 ± 0.027 ms	1.01 ± 0.61
saxpy/default/Float64/256	0.0546 ± 0.036 ms	0.0582 ± 0.035 ms	0.938 ± 0.84
saxpy/default/Float64/262144	0.181 ± 0.022 ms	0.184 ± 0.024 ms	0.985 ± 0.18
saxpy/default/Float64/32768	0.0674 ± 0.031 ms	0.0785 ± 0.032 ms	0.858 ± 0.52
saxpy/default/Float64/4096	0.0673 ± 0.026 ms	0.0671 ± 0.026 ms	1 ± 0.55
saxpy/default/Float64/512	0.0604 ± 0.035 ms	0.0582 ± 0.035 ms	1.04 ± 0.87
saxpy/default/Float64/64	0.057 ± 0.035 ms	0.06 ± 0.035 ms	0.951 ± 0.81
saxpy/default/Float64/65536	0.0878 ± 0.029 ms	0.0953 ± 0.03 ms	0.92 ± 0.41
saxpy/static workgroup=(1024,)/Float32/1024	0.0578 ± 0.035 ms	0.0588 ± 0.035 ms	0.983 ± 0.84
saxpy/static workgroup=(1024,)/Float32/1048576	0.46 ± 0.023 ms	0.459 ± 0.022 ms	1 ± 0.071
saxpy/static workgroup=(1024,)/Float32/16384	0.0524 ± 0.028 ms	0.0524 ± 0.029 ms	0.998 ± 0.76
saxpy/static workgroup=(1024,)/Float32/2048	0.0622 ± 0.026 ms	0.0617 ± 0.026 ms	1.01 ± 0.6
saxpy/static workgroup=(1024,)/Float32/256	0.0534 ± 0.035 ms	0.055 ± 0.036 ms	0.971 ± 0.9
saxpy/static workgroup=(1024,)/Float32/262144	0.167 ± 0.031 ms	0.166 ± 0.03 ms	1 ± 0.26
saxpy/static workgroup=(1024,)/Float32/32768	0.0579 ± 0.029 ms	0.0579 ± 0.029 ms	1 ± 0.71
saxpy/static workgroup=(1024,)/Float32/4096	0.0665 ± 0.024 ms	0.0661 ± 0.025 ms	1.01 ± 0.53
saxpy/static workgroup=(1024,)/Float32/512	0.0542 ± 0.035 ms	0.063 ± 0.033 ms	0.86 ± 0.72
saxpy/static workgroup=(1024,)/Float32/64	0.0581 ± 0.035 ms	0.0613 ± 0.034 ms	0.949 ± 0.78
saxpy/static workgroup=(1024,)/Float32/65536	0.0802 ± 0.03 ms	0.0828 ± 0.031 ms	0.968 ± 0.51
saxpy/static workgroup=(1024,)/Float64/1024	0.0594 ± 0.032 ms	0.0596 ± 0.031 ms	0.997 ± 0.75
saxpy/static workgroup=(1024,)/Float64/1048576	0.48 ± 0.019 ms	0.483 ± 0.019 ms	0.994 ± 0.056
saxpy/static workgroup=(1024,)/Float64/16384	0.067 ± 0.028 ms	0.0659 ± 0.029 ms	1.02 ± 0.62
saxpy/static workgroup=(1024,)/Float64/2048	0.0636 ± 0.026 ms	0.0621 ± 0.026 ms	1.03 ± 0.61
saxpy/static workgroup=(1024,)/Float64/256	0.0579 ± 0.035 ms	0.0565 ± 0.035 ms	1.02 ± 0.9
saxpy/static workgroup=(1024,)/Float64/262144	0.173 ± 0.03 ms	0.175 ± 0.029 ms	0.987 ± 0.24
saxpy/static workgroup=(1024,)/Float64/32768	0.0697 ± 0.03 ms	0.0754 ± 0.031 ms	0.924 ± 0.54
saxpy/static workgroup=(1024,)/Float64/4096	0.0655 ± 0.025 ms	0.0657 ± 0.024 ms	0.997 ± 0.52
saxpy/static workgroup=(1024,)/Float64/512	0.0602 ± 0.034 ms	0.0596 ± 0.034 ms	1.01 ± 0.82
saxpy/static workgroup=(1024,)/Float64/64	0.0586 ± 0.035 ms	0.0589 ± 0.034 ms	0.994 ± 0.83
saxpy/static workgroup=(1024,)/Float64/65536	0.0868 ± 0.03 ms	0.0929 ± 0.03 ms	0.934 ± 0.45
time_to_load	1.11 ± 0.016 s	1.13 ± 0.018 s	0.987 ± 0.021

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).