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

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Date:	Thu, 25 Aug 2011 16:20:20 +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,
	Oleg Nesterov <oleg@...hat.com>, Jiri Olsa <jolsa@...hat.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_event_task_sched_out(struct task_struct
> *prev,
> +                                            struct task_struct *next)
>  {
>         perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, NULL, 0);
>  
> -       __perf_event_task_sched_out(task, next);
> +       if (static_branch(&perf_sched_events))
> +               __perf_event_task_sched_out(prev, next);
>  } 

Right, so the reason we removed the static branch from there is

  lkml.kernel.org/r/20110324164436.GC1930@...sa.brq.redhat.com

now I think the series 075e0b0085 to 64ce312618e should have cured that
problem, and adding the static_branch() is now safe again. But there's
no mention of any of this in the Changelog.

Also, the adding back of the static_branch() is mostly unrelated to the
rest of the patch, which I shall now stare at :-)
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