1. 08 Aug, 2023 1 commit
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  3. 25 Jul, 2023 1 commit
    • Tejun Heo's avatar
      workqueue: Scale up wq_cpu_intensive_thresh_us if BogoMIPS is below 4000 · aa6fde93
      Tejun Heo authored
      wq_cpu_intensive_thresh_us is used to detect CPU-hogging per-cpu work items.
      Once detected, they're excluded from concurrency management to prevent them
      from blocking other per-cpu work items. If CONFIG_WQ_CPU_INTENSIVE_REPORT is
      enabled, repeat offenders are also reported so that the code can be updated.
      
      The default threshold is 10ms which is long enough to do fair bit of work on
      modern CPUs while short enough to be usually not noticeable. This
      unfortunately leads to a lot of, arguable spurious, detections on very slow
      CPUs. Using the same threshold across CPUs whose performance levels may be
      apart by multiple levels of magnitude doesn't make whole lot of sense.
      
      This patch scales up wq_cpu_intensive_thresh_us upto 1 second when BogoMIPS
      is below 4000. This is obviously very inaccurate but it doesn't have to be
      accurate to be useful. The mechanism is still useful when the threshold is
      fully scaled up and the benefits of reports are usually shared with everyone
      regardless of who's reporting, so as long as there are sufficient number of
      fast machines reporting, we don't lose much.
      
      Some (or is it all?) ARM CPUs systemtically report significantly lower
      BogoMIPS. While this doesn't break anything, given how widespread ARM CPUs
      are, it's at least a missed opportunity and it probably would be a good idea
      to teach workqueue about it.
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Reported-and-Tested-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
      aa6fde93
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