linux-kernel - Re: [PATCH] perf_events: improve task_sched

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Date:	Thu, 11 Mar 2010 09:35:16 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	eranian@...gle.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	fweisbec@...il.com, robert.richter@....com, davem@...emloft.net,
	perfmon2-devel@...ts.sf.net
Subject: Re: [PATCH] perf_events: improve task_sched_in()

On Wed, 2010-03-10 at 22:26 -0800, eranian@...gle.com wrote:
> This patch is an optimization in perf_event_task_sched_in() to avoid scheduling
> the events twice in a row. Without it, the perf_disable()/perf_enable() pair
> is invoked twice, thereby pinned events counts while scheduling flexible events
> and we go throuh hw_perf_enable() twice. By encapsulating, the whole sequence
> into perf_disable()/perf_enable() we ensure, hw_perf_enable() is going to be
> invoked only once because of the refcount protection.

Agreed, this makes perfect sense.

Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> --
>  perf_event.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -1382,6 +1382,8 @@ void perf_event_task_sched_in(struct task_struct *task)
>  	if (cpuctx->task_ctx == ctx)
>  		return;
>  
> +	perf_disable();
> +
>  	/*
>  	 * We want to keep the following priority order:
>  	 * cpu pinned (that don't need to move), task pinned,
> @@ -1394,6 +1396,8 @@ void perf_event_task_sched_in(struct task_struct *task)
>  	ctx_sched_in(ctx, cpuctx, EVENT_FLEXIBLE);
>  
>  	cpuctx->task_ctx = ctx;
> +
> +	perf_enable();
>  }
>  
>  #define MAX_INTERRUPTS (~0ULL)

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