linux-kernel - Re: [RFC] sched: update rq clock when only get preempt

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Date:	Mon, 30 Dec 2013 05:08:28 +0100
From:	Mike Galbraith <bitbucket@...ine.de>
To:	Lei Wen <adrian.wenl@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, leiwen@...vell.com
Subject: Re: [RFC] sched: update rq clock when only get preempt

On Mon, 2013-12-30 at 11:14 +0800, Lei Wen wrote: 
> Since we would update rq clock at task enqueue/dequeue, or schedule
> tick. If we don't update the rq clock when our previous task get
> preempted, our new started task would get a relative stale rq clock
> which is updated during the previous task enqueue, or the last schedule
> clock update.

> @@ -2555,6 +2556,8 @@ need_resched:
>                 idle_balance(cpu, rq);
> 
>         put_prev_task(rq, prev);
> +       if (update)
> +               update_rq_clock(rq);

If prev remained enqueued, the clock was updated by put_prev_task().

-Mike

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