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

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Date:	Thu, 1 Aug 2013 16:38:57 +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 08/18] sched: Reschedule task on preferred NUMA node once
 selected

On Thu, Aug 01, 2013 at 10:17:57AM +0530, Srikar Dronamraju wrote:
> * Mel Gorman <mgorman@...e.de> [2013-07-15 16:20:10]:
> 
> > A preferred node is selected based on the node the most NUMA hinting
> > faults was incurred on. There is no guarantee that the task is running
> > on that node at the time so this patch rescheules the task to run on
> > the most idle CPU of the selected node when selected. This avoids
> > waiting for the balancer to make a decision.
> > 
> > Signed-off-by: Mel Gorman <mgorman@...e.de>
> > ---
> >  kernel/sched/core.c  | 17 +++++++++++++++++
> >  kernel/sched/fair.c  | 46 +++++++++++++++++++++++++++++++++++++++++++++-
> >  kernel/sched/sched.h |  1 +
> >  3 files changed, 63 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 5e02507..b67a102 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -4856,6 +4856,23 @@ fail:
> >  	return ret;
> >  }
> > 
> > +#ifdef CONFIG_NUMA_BALANCING
> > +/* Migrate current task p to target_cpu */
> > +int migrate_task_to(struct task_struct *p, int target_cpu)
> > +{
> > +	struct migration_arg arg = { p, target_cpu };
> > +	int curr_cpu = task_cpu(p);
> > +
> > +	if (curr_cpu == target_cpu)
> > +		return 0;
> > +
> > +	if (!cpumask_test_cpu(target_cpu, tsk_cpus_allowed(p)))
> > +		return -EINVAL;
> > +
> > +	return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
> 
> As I had noted earlier, this upsets schedstats badly.
> Can we add a TODO for this patch, which mentions that schedstats need to
> taken care.
> 

I added a TODO comment because there is a possibility that this will all
change again with the stop_two_cpus patch.

-- 
Mel Gorman
SUSE Labs
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