linux-kernel - Re: [PATCH] sched: Initialize rq->age

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Message-ID: <20140509091245.GN30445@twins.programming.kicks-ass.net>
Date:	Fri, 9 May 2014 11:12:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	minyard@....org
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Corey Minyard <cminyard@...sta.com>
Subject: Re: [PATCH] sched: Initialize rq->age_stamp on processor start

On Thu, May 08, 2014 at 01:47:39PM -0500, minyard@....org wrote:
> From: Corey Minyard <cminyard@...sta.com>
> 
> If the sched_clock time starts at a large value, the kernel will spin
> in sched_avg_update for a long time while rq->age_stamp catches up
> with rq->clock.
> 
> The comment in kernel/sched/clock.c says that there is no strict promise
> that it starts at zero.  So initialize rq->age_stamp when a cpu starts up
> to avoid this.
> 
> I was seeing long delays on a simulator that didn't start the clock at
> zero.  This might also be an issue on reboots on processors that don't
> re-initialize the timer to zero on reset, and when using kexec.
> 
> Signed-off-by: Corey Minyard <cminyard@...sta.com>

Thanks

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