Messages in this thread | | | Subject | Re: Oprofile Regression Caused by commit e5d1367f17ba6a6fed5fd8b74e4d5720923e0c25 on PPC | From | Peter Zijlstra <> | Date | Tue, 11 Oct 2011 09:44:55 +0200 |
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On Mon, 2011-10-10 at 19:38 -0400, Eric B Munson wrote: > On Fri, 07 Oct 2011, Eric B Munson wrote: > > > This commit seems to have caused a regression with oprofile. It is fairly easy > > to trigger, simply run oprofile monitoring an event that will fire (something > > frequent like CPU cycles) causes oprofile to fail saying that the PMU is in use. > > If I disable CONFIG_CGROUP_PERF, everything goes back to working. I suspect the > > problem is that the PMU is being initialized without being reserved for perf. I > > am not yet sure of the right fix yet so if you have any suggestions I would > > appreciate them. > > > > Eric > > This isn't the best description of the behavior we see, what happens is at some > point in the profiling session the MMCR register is clobbered by > perf_cgroup_switch() which calls perf_pmu_enable() without reserving the PMC > hardware. When this happens oprofile stops counting. It doesn't happen each > time so some runs show event counts that are reasonable, but it can also lead to > event counts that are smaller than expected, or completely missing.
What kernel are you testing?
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