Messages in this thread | | | Date | Tue, 11 Oct 2011 09:34:09 -0400 | From | Eric B Munson <> | Subject | Re: Oprofile Regression Caused by commit e5d1367f17ba6a6fed5fd8b74e4d5720923e0c25 on PPC |
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On Tue, 11 Oct 2011, Stephane Eranian wrote:
> On Tue, Oct 11, 2011 at 9:44 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > 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? > > > Looking at 3.1-rc9, I doubt it's coming from perf_cgroup_switch(). The function > is checking for perf context with at least of cgroup event before > calling perf_pmu_disable(). > If there is no active perf context, there is no cgroup event, thus the > function is a nop. > Even if you have a competing perf session, it would have to have at > least one cgroup > event for this code to touch HW. The problem must come from somewhere else. > > > >
Does activating any cgroup setup a cgroup event?
Eric [unhandled content-type:application/pgp-signature] | |