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Date: Thu, 4 Jul 2013 16:06:13 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mel Gorman <mgorman@suse.de>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, Andrea Arcangeli <aarcange@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 13/13] sched: Account for the number of preferred tasks
 running on a node when selecting a preferred node
Message-ID: <20130704140612.GO18898@dyad.programming.kicks-ass.net>
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On Thu, Jul 04, 2013 at 02:54:15PM +0100, Mel Gorman wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 9247345..387f28d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -863,9 +863,13 @@ find_idlest_cpu_node(int this_cpu, int nid)
>  		load = weighted_cpuload(i);
>  
>  		if (load < min_load) {
> -			/* Do not preempt a task running on a preferred node */
> +			/*
> +			 * Do not preempt a task running on a preferred node or
> +			 * tasks are are pinned to their current CPU
> +			 */
>  			struct task_struct *p = cpu_rq(i)->curr;
> -			if (p->numa_preferred_nid != nid) {
> +			if (p->numa_preferred_nid != nid &&
> +			    cpumask_weight(tsk_cpus_allowed(p)) > 1) {

We have p->nr_cpus_allowed for that.

>  				min_load = load;
>  				idlest_cpu = i;
>  			}