linux-kernel - Re: [PATCH] sched: update_rq_clock() must skip ONE update

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Message-ID: <20140331160003.GD19658@home.goodmis.org>
Date:	Mon, 31 Mar 2014 12:00:03 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: update_rq_clock() must skip ONE update

On Mon, Mar 31, 2014 at 06:20:36AM +0200, Mike Galbraith wrote:
> 
> Cc: <stable@...r.kernel.org>
> Signed-off-by: 	Mike Galbraith <umgwanakikbuti@...il.com>
> ---
>  kernel/sched/core.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -118,7 +118,7 @@ void update_rq_clock(struct rq *rq)
>  {
>  	s64 delta;
>  

Mike,

If I understand this code correctly, skip_clock_update gets set to one,
where it should skip the next call to update_rq_clock(), but only the
next skip_clock_update(), and after that, it should resume calling it again.
Is that correct?

If so, can we add a comment here stating such. For example:

/*
 * rq->skip_clock_update gets set to "1" to skip the next clock update.
 * The following calls should continue to do the update unless
 * rq->skip_clock_update gets set to "1" again.
 */

?

-- Steve

> -	if (rq->skip_clock_update > 0)
> +	if (rq->skip_clock_update-- > 0)
>  		return;
>  
>  	delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
> 
> 
> 
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