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Message-ID: <1431954418.3322.3.camel@twins>
Subject: Re: [RFC][PATCH 4/4] sched, numa: Ignore pinned tasks
From: Peter Zijlstra <peterz@infradead.org>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: mingo@kernel.org, riel@redhat.com, dedekind1@gmail.com,
        linux-kernel@vger.kernel.org, mgorman@suse.de, rostedt@goodmis.org,
        juri.lelli@arm.com
Date: Mon, 18 May 2015 15:06:58 +0200
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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?