linux-kernel - Re: [PATCH] sched,numa: ensure task_numa

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Message-ID: <20140606154301.GD11371@laptop.programming.kicks-ass.net>
Date:	Fri, 6 Jun 2014 17:43:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-kernel@...r.kernel.org, mgorman@...e.de, mingo@...nel.org
Subject: Re: [PATCH] sched,numa: ensure task_numa_migrate checks the
 preferred node

On Wed, Jun 04, 2014 at 04:09:42PM -0400, Rik van Riel wrote:
> The first thing task_numa_migrate does is check to see if there is
> CPU capacity available on the preferred node, in order to move the
> task there.
> 
> However, if the preferred node is all busy, we would skip considering
> that node for tasks swaps in the subsequent loop. This prevents NUMA
> convergence of tasks on busy systems.
> 
> However, swapping locations with a task on our preferred nid, when
> the preferred nid is busy, is perfectly fine.
> 
> The fix is to also look for a CPU on our preferred nid when it is
> totally busy.
> 
> This changes "perf bench numa mem -p 4 -t 20 -m -0 -P 1000" from
> not converging in 15 minutes on my 4 node system, to converging in
> 10-20 seconds.
> 
> Signed-off-by: Rik van Riel <riel@...hat.com>


Indeed so. Thanks Rik!

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