From: Anton Blanchard Date: Mon, 17 Jan 2011 05:17:42 +0000 (+1100) Subject: powerpc: perf: Fix frequency calculation for overflowing counters X-Git-Tag: MMI-PSA29.97-13-9~20972^2~5 X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=4bca770ede796a1ef7af9c983166d5608d9ccfaf;p=GitHub%2FMotorolaMobilityLLC%2Fkernel-slsi.git 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 Acked-by: Benjamin Herrenschmidt Cc: linuxppc-dev@lists.ozlabs.org Cc: Paul Mackerras Cc: Peter Zijlstra Cc: Arnaldo Carvalho de Melo LKML-Reference: <20110117161742.5feb3761@kryten> Signed-off-by: Ingo Molnar --- 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;