scx_bpfland: prevent per-CPU DSQ stall with per-CPU kthreads #755
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Since per-CPU kthreads may show an inconsistent prev_cpu and/or cpumask, dispatch them directly to local DSQ and allow to preempt the current running task. This allows to prevent per-CPU kthread stalls and it also helps to prioritize them, as are usually important for system performance and responsiveness. Moreover, change the behavior of --local-kthreads to prioritize all kthreads when this option is used. This addresses issue #728. NOTE: ideally we may want to fix this in the kernel by making sure to always expose a consistent prev_cpu and cpumask also for kthreads, but at the moment this change allows to prevent some annoying stalls and performance-wise it doesn't seem to introduce any regression. In fact, the usual gaming/fps benchmarks show even a slight improvement in responsiveness with this change applied. Thanks to YUBY from the CachyOS community for all the extremely valuable help with the intensive stress tests. Signed-off-by: Andrea Righi <[email protected]>
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sirlucjan
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Since per-CPU kthreads may show an inconsistent prev_cpu and/or cpumask, dispatch them directly to local DSQ and allow to preempt the current running task.
This allows to prevent per-CPU kthread stalls and it also helps to prioritize them, as are usually important for system performance and responsiveness.
Moreover, change the behavior of --local-kthreads to prioritize all kthreads when this option is used.
This addresses issue #728.
NOTE: ideally we may want to fix this in the kernel by making sure to always expose a consistent prev_cpu and cpumask also for kthreads, but at the moment this change allows to prevent some annoying stalls and performance-wise it doesn't seem to introduce any regression. In fact, the usual gaming/fps benchmarks show even a slight improvement in responsiveness with this change applied.