Re: [PATCH] powerpc: perf: Fix frequency calculation for overflowing counters
From: Scott Wood <hidden>
Date: 2011-01-17 17:33:08
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On Mon, 17 Jan 2011 16:17:42 +1100 Anton Blanchard [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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 <redacted> ---diff --git a/arch/powerpc/kernel/perf_event.c b/arch/powerpc/kernel/perf_event.c index 5674807..ab6f6be 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;_______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Does perf_event_fsl_emb.c need this as well (it has almost the same record_and_restart code)? -Scott