linux-kernel - Re: [PATCH 14/15] sched: Account for the number of preferred tasks running on a node when selecting a preferred node

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Date:	Sat, 6 Jul 2013 12:46:14 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 14/15] sched: Account for the number of preferred tasks
 running on a node when selecting a preferred node

On Sat, Jul 06, 2013 at 12:09:01AM +0100, Mel Gorman wrote:
> +/* Returns true if the given node is compute overloaded */
> +static bool sched_numa_overloaded(int nid)
> +{
> +	int nr_cpus = 0;
> +	int nr_preferred = 0;
> +	int i;
> +
> +	for_each_cpu(i, cpumask_of_node(nid)) {
> +		nr_cpus++;
> +		nr_preferred += cpu_rq(i)->nr_preferred_running;
> +	}
> +
> +	return nr_preferred >= nr_cpus << 1;
> +}
> +
>  static void task_numa_placement(struct task_struct *p)
>  {
>  	int seq, nid, max_nid = 0;
> @@ -908,7 +935,7 @@ static void task_numa_placement(struct task_struct *p)
>  
>  		/* Find maximum private faults */
>  		faults = p->numa_faults[task_faults_idx(nid, 1)];
> -		if (faults > max_faults) {
> +		if (faults > max_faults && !sched_numa_overloaded(nid)) {
>  			max_faults = faults;
>  			max_nid = nid;
>  		}

This again very explicitly breaks for overloaded scenarios.
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