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

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Message-ID: <536BD141.7030000@mvista.com>
Date:	Thu, 08 May 2014 13:47:29 -0500
From:	Corey Minyard <cminyard@...sta.com>
To:	Peter Zijlstra <peterz@...radead.org>, minyard@....org
CC:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: Initialize rq->age_stamp on processor start

On 05/08/2014 11:13 AM, Peter Zijlstra wrote:
> On Tue, May 06, 2014 at 02:50:57PM -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>
> This patch made my cris-defconfig build fail.
Dang, I missed propagating a change.  Yes, it's broken.  One more time...

-corey
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