linux-kernel - Re: [PATCH 08/18] sched: Reschedule task on preferred NUMA node once selected

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Date:	Wed, 17 Jul 2013 09:31:05 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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 08/18] sched: Reschedule task on preferred NUMA node once selected

On Mon, Jul 15, 2013 at 11:20 PM, Mel Gorman <mgorman@...e.de> wrote:
> +static int
> +find_idlest_cpu_node(int this_cpu, int nid)
> +{
> +       unsigned long load, min_load = ULONG_MAX;
> +       int i, idlest_cpu = this_cpu;
> +
> +       BUG_ON(cpu_to_node(this_cpu) == nid);
> +
> +       rcu_read_lock();
> +       for_each_cpu(i, cpumask_of_node(nid)) {

Check allowed CPUs first if task is given?

> +               load = weighted_cpuload(i);
> +
> +               if (load < min_load) {
> +                       min_load = load;
> +                       idlest_cpu = i;
> +               }
> +       }
> +       rcu_read_unlock();
> +
> +       return idlest_cpu;
> +}
> +
[...]
> +       /*
> +        * Record the preferred node as the node with the most faults,
> +        * requeue the task to be running on the idlest CPU on the
> +        * preferred node and reset the scanning rate to recheck
> +        * the working set placement.
> +        */
>         if (max_faults && max_nid != p->numa_preferred_nid) {
> +               int preferred_cpu;
> +
> +               /*
> +                * If the task is not on the preferred node then find the most
> +                * idle CPU to migrate to.
> +                */
> +               preferred_cpu = task_cpu(p);
> +               if (cpu_to_node(preferred_cpu) != max_nid) {
> +                       preferred_cpu = find_idlest_cpu_node(preferred_cpu,
> +                                                            max_nid);
> +               }
> +
> +               /* Update the preferred nid and migrate task if possible */
>                 p->numa_preferred_nid = max_nid;
>                 p->numa_migrate_seq = 0;
> +               migrate_task_to(p, preferred_cpu);
>         }
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