linux-kernel - Re: [PATCH] perf_event: fix slow and broken cgroup context switch code

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Date:	Thu, 25 Aug 2011 16:26:14 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, ming.m.lin@...el.com
Subject: Re: [PATCH] perf_event: fix slow and broken cgroup context switch
 code

On Thu, 2011-08-25 at 15:58 +0200, Stephane Eranian wrote:
> +static inline void perf_cgroup_sched_out(struct task_struct *task,
> +                                        struct task_struct *next)
>  {
> +       struct perf_cgroup *cgrp1;
> +       struct perf_cgroup *cgrp2 = NULL;
> +
> +       /*
> +        * we come here when we know perf_cgroup_events > 0
> +        */
> +       cgrp1 = perf_cgroup_from_task(task);
> +
> +       /*
> +        * next is NULL when called from perf_event_enable_on_exec()
> +        * that will systematically cause a cgroup_switch()
> +        */
> +       if (next)
> +               cgrp2 = perf_cgroup_from_task(next);
> +
> +       /*
> +        * only schedule out current cgroup events if we know
> +        * that we are switching to a different cgroup. Otherwise,
> +        * do no touch the cgroup events.
> +        */
> +       if (cgrp1 != cgrp2)
> +               perf_cgroup_switch(task, PERF_CGROUP_SWOUT);
>  }
>  
> +static inline void perf_cgroup_sched_in(struct task_struct *prev,
> +                                       struct task_struct *task)
>  {
> +       struct perf_cgroup *cgrp1;
> +       struct perf_cgroup *cgrp2 = NULL;
> +
> +       /*
> +        * we come here when we know perf_cgroup_events > 0
> +        */
> +       cgrp1 = perf_cgroup_from_task(task);
> +
> +       /* prev can never be NULL */
> +       cgrp2 = perf_cgroup_from_task(prev);
> +
> +       /*
> +        * only need to schedule in cgroup events if we are changing
> +        * cgroup during ctxsw. Cgroup events were not scheduled
> +        * out of ctxsw out if that was not the case.
> +        */
> +       if (cgrp1 != cgrp2)
> +               perf_cgroup_switch(task, PERF_CGROUP_SWIN);
>  } 

OK, looks sane enough, queued the patch, thanks!
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