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SubjectRe: Oprofile Regression Caused by commit e5d1367f17ba6a6fed5fd8b74e4d5720923e0c25 on PPC
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Hi,

I suspect it's because of this chunk:
rcu_read_lock();

list_for_each_entry_rcu(pmu, &pmus, entry) {
-
cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);

- perf_pmu_disable(cpuctx->ctx.pmu);
-
/*
* perf_cgroup_events says at least one
* context on this CPU has cgroup events.
@@ -353,6 +366,8 @@ void perf_cgroup_switch(struct task_struct *task, int mode)
* events for a context.
*/
if (cpuctx->ctx.nr_cgroups > 0) {
+ perf_ctx_lock(cpuctx, cpuctx->task_ctx);
+ perf_pmu_disable(cpuctx->ctx.pmu);


In other words, you don't call perf_pmu_disable() unless you know
you have cgroup events.

Without that, I think you will touch the PMU on cgroup switch and
that night conflict with another subsystem using the PMU, e.g. OProfile.

On Tue, Oct 18, 2011 at 4:43 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> On Tue, 2011-10-18 at 09:53 -0400, Eric B Munson wrote:
>> On Wed, 12 Oct 2011, Stephane Eranian wrote:
>>
>> > Could be:
>> >    a8d757e perf events: Fix slow and broken cgroup context switch code
>> >
>>
>> Thanks for the pointer, but the fix was in:
>>     facc4307 perf: Optimize event scheduling locking
>>
>> This might be a candidate for stable given that oprofile is broken without it.
>
> I might feel much more confident about recommending that if someone
> could explain why that patches fixes what exact problem.
>
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