linux-kernel - RE: [rfc patch] Re: sched: incorrect argument used in task

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Date:	Fri, 17 Nov 2006 11:41:51 -0800
From:	"Chen, Kenneth W" <kenneth.w.chen@...el.com>
To:	"'Ingo Molnar'" <mingo@...e.hu>, "Mike Galbraith" <efault@....de>
Cc:	<nickpiggin@...oo.com.au>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	<linux-kernel@...r.kernel.org>, "Andrew Morton" <akpm@...l.org>
Subject: RE: [rfc patch] Re: sched: incorrect argument used in task_hot()

Ingo Molnar wrote on Friday, November 17, 2006 11:21 AM
> * Mike Galbraith <efault@....de> wrote:
> 
> > One way to improve granularity, and eliminate the possibility of 
> > p->last_run being > rq->timestamp_tast_tick, and thereby short 
> > circuiting the evaluation of cache_hot_time, is to cache the last 
> > return of sched_clock() at both tick and sched times, and use that 
> > value as our reference instead of the absolute time of the tick.  It 
> > won't totally eliminate skew, but it moves the reference point closer 
> > to the current time on the remote cpu.
> > 
> > Looking for a good place to do this, I chose update_cpu_clock().
> 
> looks good to me - thus we will update the timestamp not only in the 
> timer tick, but also upon every context-switch (when we acquire 
> sched_clock() value anyway). Lets try this in -mm?

Certainly gets my vote.  For my particular workload environment, there
are enough schedule activity on the remote CPU and in theory it should
make time calculation a lot better than what it is now.  I will run a
couple of experiment to verify.

Acked-by: Ken Chen <kenneth.w.chen@...el.com>

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