linux-kernel - Re: [PATCH 17/18] sched: Add tracepoints related to NUMA task migration

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Message-ID: <20131211083744.GP11295@suse.de>
Date:	Wed, 11 Dec 2013 08:37:45 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alex Thorlton <athorlton@....com>, Rik van Riel <riel@...hat.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 17/18] sched: Add tracepoints related to NUMA task
 migration

On Tue, Dec 10, 2013 at 02:22:11PM -0800, Andrew Morton wrote:
> On Tue, 10 Dec 2013 15:51:35 +0000 Mel Gorman <mgorman@...e.de> wrote:
> 
> > This patch adds three tracepoints
> >  o trace_sched_move_numa	when a task is moved to a node
> >  o trace_sched_swap_numa	when a task is swapped with another task
> >  o trace_sched_stick_numa	when a numa-related migration fails
> > 
> > The tracepoints allow the NUMA scheduler activity to be monitored and the
> > following high-level metrics can be calculated
> > 
> >  o NUMA migrated stuck	 nr trace_sched_stick_numa
> >  o NUMA migrated idle	 nr trace_sched_move_numa
> >  o NUMA migrated swapped nr trace_sched_swap_numa
> >  o NUMA local swapped	 trace_sched_swap_numa src_nid == dst_nid (should never happen)
> >  o NUMA remote swapped	 trace_sched_swap_numa src_nid != dst_nid (should == NUMA migrated swapped)
> >  o NUMA group swapped	 trace_sched_swap_numa src_ngid == dst_ngid
> > 			 Maybe a small number of these are acceptable
> > 			 but a high number would be a major surprise.
> > 			 It would be even worse if bounces are frequent.
> >  o NUMA avg task migs.	 Average number of migrations for tasks
> >  o NUMA stddev task mig	 Self-explanatory
> >  o NUMA max task migs.	 Maximum number of migrations for a single task
> > 
> > In general the intent of the tracepoints is to help diagnose problems
> > where automatic NUMA balancing appears to be doing an excessive amount of
> > useless work.
> > 
> > ...
> >
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -1272,11 +1272,13 @@ static int task_numa_migrate(struct task_struct *p)
> >  	p->numa_scan_period = task_scan_min(p);
> >  
> >  	if (env.best_task == NULL) {
> > -		int ret = migrate_task_to(p, env.best_cpu);
> > +		if ((ret = migrate_task_to(p, env.best_cpu)) != 0)
> > +			trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
> >  		return ret;
> >  	}
> >  
> > -	ret = migrate_swap(p, env.best_task);
> > +	if ((ret = migrate_swap(p, env.best_task)) != 0);
> 
> I'll zap that semicolon...
> 

Thanks

-- 
Mel Gorman
SUSE Labs
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