linux-kernel - Re: [PATCH 3/3] perf_event: cleanup for cpu_clock_perf_event

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Date:	Wed, 9 Dec 2009 09:54:19 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] perf_event: cleanup for
	cpu_clock_perf_event_update()

On Wed, Dec 09, 2009 at 11:30:36AM +0800, Xiao Guangrong wrote:
> Using atomic64_xchg() instead of atomic64_read() and atomic64_set().
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
> ---
>  kernel/perf_event.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> index 592b293..8f46012 100644
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -4079,8 +4079,7 @@ static void cpu_clock_perf_event_update(struct perf_event *event)
>  	u64 now;
>  
>  	now = cpu_clock(cpu);
> -	prev = atomic64_read(&event->hw.prev_count);
> -	atomic64_set(&event->hw.prev_count, now);
> +	prev = atomic64_xchg(&event->hw.prev_count, now);
>  	atomic64_add(now - prev, &event->count);
>  }


Reviewed-by: Frederic Weisbecker <fweisbec@...il.com>

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