linux-kernel - Re: [RFC][PATCH 25/26] sched, numa: Only migrate long-running entities

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Date:	Mon, 09 Jul 2012 16:55:58 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Rik van Riel <riel@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dan Smith <danms@...ibm.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC][PATCH 25/26] sched, numa: Only migrate long-running
 entities

On Mon, 2012-07-09 at 10:53 -0400, Rik van Riel wrote:
> On 07/09/2012 08:26 AM, Peter Zijlstra wrote:
> > On Sun, 2012-07-08 at 14:34 -0400, Rik van Riel wrote:
> 
> >> Do we really want to calculate the amount of CPU time used
> >> by a process, and start migrating after just one second?
> >>
> >> Or would it be ok to start migrating once a process has
> >> been scanned once or twice by the NUMA code?
> >
> > You mean, the 2-3rd time we try and migrate this task, not the memory
> > scanning thing as per Andrea, right?
> 
> Indeed.  That way we can simply keep a flag somewhere,
> instead of iterating over the threads in a process.

Note that the code in -tip needs to iterate over all tasks in order to
test all cpus_allowed and mems_allowed masks. But we could keep a
process wide intersection of those masks around as well I guess,
updating them is a slow path anyway.
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