linux-kernel - Re: [LKP] [sched/numa] a43455a1d57: +94.1% proc-vmstat.numa_hint_faults

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Message-ID: <20140731050454.GA9386@aaronlu.sh.intel.com>
Date:	Thu, 31 Jul 2014 13:04:54 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org,
	jhladky@...hat.com
Subject: Re: [LKP] [sched/numa] a43455a1d57: +94.1%
 proc-vmstat.numa_hint_faults_local

On Wed, Jul 30, 2014 at 10:25:03AM -0400, Rik van Riel wrote:
> On 07/29/2014 10:14 PM, Aaron Lu wrote:
> > On Tue, Jul 29, 2014 at 04:04:37PM -0400, Rik van Riel wrote:
> >> On Tue, 29 Jul 2014 10:17:12 +0200
> >> Peter Zijlstra <peterz@...radead.org> wrote:
> >>
> >>>> +#define NUMA_SCALE 1000
> >>>> +#define NUMA_MOVE_THRESH 50
> >>>
> >>> Please make that 1024, there's no reason not to use power of two here.
> >>> This base 10 factor thing annoyed me no end already, its time for it to
> >>> die.
> >>
> >> That's easy enough.  However, it would be good to know whether
> >> this actually helps with the regression Aaron found :)
> > 
> > Sorry for the delay.
> > 
> > I applied the last patch and queued the hackbench job to the ivb42 test
> > machine for it to run 5 times, and here is the result(regarding the
> > proc-vmstat.numa_hint_faults_local field):
> > 173565
> > 201262
> > 192317
> > 198342
> > 198595
> > avg:
> > 192816
> > 
> > It seems it is still very big than previous kernels.
> 
> It looks like a step in the right direction, though.
> 
> Could you try running with a larger threshold?
> 
> >> +++ b/kernel/sched/fair.c
> >> @@ -924,10 +924,12 @@ static inline unsigned long group_faults_cpu(struct numa_group *group, int nid)
> >>  
> >>  /*
> >>   * These return the fraction of accesses done by a particular task, or
> >> - * task group, on a particular numa node.  The group weight is given a
> >> - * larger multiplier, in order to group tasks together that are almost
> >> - * evenly spread out between numa nodes.
> >> + * task group, on a particular numa node.  The NUMA move threshold
> >> + * prevents task moves with marginal improvement, and is set to 5%.
> >>   */
> >> +#define NUMA_SCALE 1024
> >> +#define NUMA_MOVE_THRESH (5 * NUMA_SCALE / 100)
> 
> It would be good to see if changing NUMA_MOVE_THRESH to
> (NUMA_SCALE / 8) does the trick.

With your 2nd patch and the above change, the result is:

"proc-vmstat.numa_hint_faults_local": [
  199708,
  209152,
  200638,
  187324,
  196654
  ],

avg:
198695

Regards,
Aaron
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