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  1. 07 Feb, 2012 2 commits
    • Stephane Eranian's avatar
      perf: Fix double start/stop in x86_pmu_start() · f39d47ff
      Stephane Eranian authored 
      The following patch fixes a bug introduced by the following
commit:

        e050e3f0 ("perf: Fix broken interrupt rate throttling")

The patch caused the following warning to pop up depending on
the sampling frequency adjustments:

  ------------[ cut here ]------------
  WARNING: at arch/x86/kernel/cpu/perf_event.c:995 x86_pmu_start+0x79/0xd4()

It was caused by the following call sequence:

perf_adjust_freq_unthr_context.part() {
     stop()
     if (delta > 0) {
          perf_adjust_period() {
              if (period > 8*...) {
                  stop()
                  ...
                  start()
              }
          }
      }
      start()
}

Which caused a double start and a double stop, thus triggering
the assert in x86_pmu_start().

The patch fixes the problem by avoiding the double calls. We
pass a new argument to perf_adjust_period() to indicate whether
or not the event is already stopped. We can't just remove the
start/stop from that function because it's called from
__perf_event_overflow where the event needs to be reloaded via a
stop/start back-toback call.

The patch reintroduces the assertion in x86_pmu_start() which
was removed by commit:

	84f2b9b2 ("perf: Remove deprecated WARN_ON_ONCE()")

In this second version, we've added calls to disable/enable PMU
during unthrottling or frequency adjustment based on bug report
of spurious NMI interrupts from Eric Dumazet.
Reported-and-tested-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarStephane Eranian <eranian@google.com>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: markus@trippelsdorf.de
Cc: paulus@samba.org
Link: http://lkml.kernel.org/r/20120207133956.GA4932@quad
[ Minor edits to the changelog and to the code ]
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      f39d47ff
    • Ingo Molnar's avatar
      Merge tag 'perf-urgent-for-mingo' of... · 136e0b8e
      Ingo Molnar authored 
      Merge tag 'perf-urgent-for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/urgent

Fixes for some long standing problems.
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      136e0b8e
  3. 06 Feb, 2012 3 commits
  5. 03 Feb, 2012 1 commit
    • Stephane Eranian's avatar
      perf: Remove deprecated WARN_ON_ONCE() · 84f2b9b2
      Stephane Eranian authored 
      With the new throttling/unthrottling code introduced with
commit:

  e050e3f0 ("perf: Fix broken interrupt rate throttling")

we occasionally hit two WARN_ON_ONCE() checks in:

  - intel_pmu_pebs_enable()
  - intel_pmu_lbr_enable()
  - x86_pmu_start()

The assertions are no longer problematic. There is a valid
path where they can trigger but it is harmless.

The assertion can be triggered with:

  $ perf record -e instructions:pp ....

Leading to paths:

  intel_pmu_pebs_enable
  intel_pmu_enable_event
  x86_perf_event_set_period
  x86_pmu_start
  perf_adjust_freq_unthr_context
  perf_event_task_tick
  scheduler_tick

And:

  intel_pmu_lbr_enable
  intel_pmu_enable_event
  x86_perf_event_set_period
  x86_pmu_start
  perf_adjust_freq_unthr_context.
  perf_event_task_tick
  scheduler_tick

cpuc->enabled is always on because when we get to
perf_adjust_freq_unthr_context() the PMU is not totally
disabled. Furthermore when we need to adjust a period,
we only stop the event we need to change and not the
entire PMU. Thus, when we re-enable, cpuc->enabled is
already set. Note that when we stop the event, both
pebs and lbr are stopped if necessary (and possible).
Signed-off-by: default avatarStephane Eranian <eranian@google.com>
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/20120202110401.GA30911@quadSigned-off-by: default avatarIngo Molnar <mingo@elte.hu>
      84f2b9b2
  7. 02 Feb, 2012 19 commits
  9. 01 Feb, 2012 15 commits
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