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

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Date:	Mon, 18 May 2015 15:06:58 +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, 2015-05-18 at 18:30 +0530, Srikar Dronamraju wrote:
> >  
> >  static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
> >  {
> > +	if (p->nr_cpus_allowed == 1) {
> > +		rq->nr_pinned_running--;
> > +		WARN_ON_ONCE(p->numa_preferred_nid != -1);
> > +	}
> >  	rq->nr_numa_running -= (p->numa_preferred_nid != -1);
> >  	rq->nr_preferred_running -= (p->numa_preferred_nid == task_node(p));
> >  }
> 
> 
> Shouldnt we reset p->numa_preferred_nid when we are setting the allowed
> cpus in set_cpus_allowed_common()? 
> 
> Otherwise if an process is set a preferred node based on its numa faults
> but then is pinned to a different cpu, then we can see this warning.:w!

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?


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