diff options
| author | Anton Blanchard <anton@samba.org> | 2011-01-17 16:17:42 +1100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2011-01-17 11:43:02 +0100 |
| commit | 4bca770ede796a1ef7af9c983166d5608d9ccfaf (patch) | |
| tree | 3a55c96dfb709415ee2c4e54e242c4f1a7cd01e2 /arch | |
| parent | 7c46d8da09df22361d1d43465c4f1b06cecaf25f (diff) | |
powerpc: perf: Fix frequency calculation for overflowing counters
When profiling a benchmark that is almost 100% userspace, I noticed some wildly
inaccurate profiles that showed almost all time spent in the kernel.
Closer examination shows we were programming a tiny number of cycles into the
PMU after each overflow (about ~200 away from the next overflow). This gets us
stuck in a loop which we eventually break out of by throttling the PMU (there
are regular throttle/unthrottle events in the log).
It looks like we aren't setting event->hw.last_period to something same and the
frequency to period calculations in perf are going haywire.
With the following patch we find the correct period after a few interrupts and
stay there. I also see no more throttle events.
Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
LKML-Reference: <20110117161742.5feb3761@kryten>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/powerpc/kernel/perf_event.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/perf_event.c b/arch/powerpc/kernel/perf_event.c index 567480705789..ab6f6beadb57 100644 --- a/arch/powerpc/kernel/perf_event.c +++ b/arch/powerpc/kernel/perf_event.c @@ -1212,6 +1212,7 @@ static void record_and_restart(struct perf_event *event, unsigned long val, if (left <= 0) left = period; record = 1; + event->hw.last_period = event->hw.sample_period; } if (left < 0x80000000LL) val = 0x80000000LL - left; |