linux-kernel - Re: [RFC][PATCH 4/4] sched, numa: Ignore pinned tasks

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Message-ID: <20150518150947.GA5404@twins.programming.kicks-ass.net>
Date:	Mon, 18 May 2015 17:09:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	mingo@...nel.org, riel@...hat.com, dedekind1@...il.com,
	linux-kernel@...r.kernel.org, mgorman@...e.de, rostedt@...dmis.org,
	juri.lelli@....com
Subject: Re: [RFC][PATCH 4/4] sched, numa: Ignore pinned tasks

On Mon, May 18, 2015 at 07:59:40PM +0530, Srikar Dronamraju wrote:
> > We should never get preferred_nid set when nr_cpus_allowed == 1, see the
> > hunk that changes task_tick_numa.
> > 
> > So we set preferred = -1 on pinning, do not partake in numa balancing
> > while this is so, therefore it should still be so when we dequeue,
> > right?
> 
> lets say if a thread were to do a sched_setaffinity on itself ;
> would it not call account_numa_dequeue before account_numa_enqueue?

Yes, but it would call dequeue while nr_cpus_allowed was still the 'old'
value. And it will call enqueue when its the 'new' value.

> Also setting preferred = -1 in set_cpus_allowed avoids us from setting
> it at account_numa_enqueue. account_numa_enqueue() would probably be
> called more times than set_cpus_allowed.

This is true; and that makes sense.
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