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  1. Oct 10, 2009
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  3. Oct 08, 2009
    • Arjan van de Ven's avatar
      x86, timers: Check for pending timers after (device) interrupts · 9bcbdd9c
      Arjan van de Ven authored
      
      
      Now that range timers and deferred timers are common, I found a
      problem with these using the "perf timechart" tool. Frans Pop also
      reported high scheduler latencies via LatencyTop, when using
      iwlagn.
      
      It turns out that on x86, these two 'opportunistic' timers only get
      checked when another "real" timer happens. These opportunistic
      timers have the objective to save power by hitchhiking on other
      wakeups, as to avoid CPU wakeups by themselves as much as possible.
      
      The change in this patch runs this check not only at timer
      interrupts, but at all (device) interrupts. The effect is that:
      
       1) the deferred timers/range timers get delayed less
      
       2) the range timers cause less wakeups by themselves because
          the percentage of hitchhiking on existing wakeup events goes up.
      
      I've verified the working of the patch using "perf timechart", the
      original exposed bug is gone with this patch. Frans also reported
      success - the latencies are now down in the expected ~10 msec
      range.
      
      Signed-off-by: default avatarArjan van de Ven <arjan@linux.intel.com>
      Tested-by: default avatarFrans Pop <elendil@planet.nl>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Mike Galbraith <efault@gmx.de>
      LKML-Reference: <20091008064041.67219b13@infradead.org>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      9bcbdd9c