On Mon, 17 Jan 2011 16:17:42 +1100 Anton Blanchard <an...@samba.org> wrote:
> > 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 <an...@samba.org> > --- > > 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 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
