linux-kernel - Re: [PATCH 30/31] sched, numa, mm: Implement slow start for working set sampling

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Message-ID: <20121101155226.GE3888@suse.de>
Date:	Thu, 1 Nov 2012 15:52:26 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 30/31] sched, numa, mm: Implement slow start for working
 set sampling

On Thu, Oct 25, 2012 at 02:16:47PM +0200, Peter Zijlstra wrote:
> Add a 1 second delay before starting to scan the working set of
> a task and starting to balance it amongst nodes.
> 
> [ note that before the constant per task WSS sampling rate patch
>   the initial scan would happen much later still, in effect that
>   patch caused this regression. ]
> 
> The theory is that short-run tasks benefit very little from NUMA
> placement: they come and go, and they better stick to the node
> they were started on. As tasks mature and rebalance to other CPUs
> and nodes, so does their NUMA placement have to change and so
> does it start to matter more and more.
> 

Yeah, ok. It's done by wall time, right? Should it be CPU time in case
it spent the first second asleep?

-- 
Mel Gorman
SUSE Labs
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