linux-kernel - Re: [PATCH 06/13] sched: Reschedule task on preferred NUMA node once selected

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Date:	Thu, 4 Jul 2013 14:29:39 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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 06/13] sched: Reschedule task on preferred NUMA node once
 selected

On Thu, Jul 04, 2013 at 05:56:44PM +0530, Srikar Dronamraju wrote:
> * Mel Gorman <mgorman@...e.de> [2013-07-03 15:21:33]:
> 
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 2a0bbc2..b9139be 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -800,6 +800,37 @@ unsigned int sysctl_numa_balancing_scan_delay = 1000;
> >   */
> >  unsigned int sysctl_numa_balancing_settle_count __read_mostly = 3;
> > 
> > +static unsigned long weighted_cpuload(const int cpu);
> > +
> > +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);
> > +
> > +	for_each_cpu(i, cpumask_of_node(nid)) {
> > +		load = weighted_cpuload(i);
> > +
> > +		if (load < min_load) {
> > +			struct task_struct *p;
> > +
> > +			/* Do not preempt a task running on its preferred node */
> > +			struct rq *rq = cpu_rq(i);
> > +			raw_spin_lock_irq(&rq->lock);
> 
> Not sure why we need this spin_lock? Cant this be done in a rcu block
> instead?
> 

Judging by how find_idlest_cpu works it would appear you are correct.
Thanks very much, I'm still pretty much a scheduler wuss. I know what I
want but not always how to get it :)

-- 
Mel Gorman
SUSE Labs
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