Re: [PATCH] perf cgroups: Fix perf_cgroup_switch schedule in warning

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Tue, 2012-10-02 at 13:42 +0200, Jiri Olsa wrote:
> +++ b/kernel/events/core.c
> @@ -394,7 +394,8 @@ void perf_cgroup_switch(struct task_struct *task, int mode)
>                         }
>  
>                         if (mode & PERF_CGROUP_SWIN) {
> -                               WARN_ON_ONCE(cpuctx->cgrp);
> +                               WARN_ON_ONCE(cpuctx->cgrp && !cpuctx->ctx.is_active);
> +
>                                 /* set cgrp before ctxsw in to
>                                  * allow event_filter_match() to not
>                                  * have to pass task around 

OK, like you mentioned this is the result of multiple PMU being able to
share a cpuctx, shouldn't we in that case avoid the second loop over the
cpuctx as a whole?

Would something like the below do? IIRC I introduced that active_pmu for
exactly such reasons..

---
 kernel/events/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7b9df35..e98f014 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -372,6 +372,8 @@ void perf_cgroup_switch(struct task_struct *task, int mode)
 
 	list_for_each_entry_rcu(pmu, &pmus, entry) {
 		cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+		if (cpuctx->active_pmu != pmu)
+			continue;
 
 		/*
 		 * perf_cgroup_events says at least one