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4bca770ede
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> |
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