linux-kernel - Re: [PATCH] sched/numa: use runnable

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Message-ID: <CAKfTPtBfb25L4J2tF-XOXVJSu8-N-dzU3mBdTPVxAtCnUZNfLA@mail.gmail.com>
Date:   Tue, 25 Aug 2020 17:52:38 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Mel Gorman <mgorman@...e.de>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/numa: use runnable_avg to classify node

On Tue, 25 Aug 2020 at 15:58, Mel Gorman <mgorman@...e.de> wrote:
>
> On Tue, Aug 25, 2020 at 02:18:18PM +0200, Vincent Guittot wrote:
> > Use runnable_avg to classify numa node state similarly to what is done for
> > normal load balancer. This helps to ensure that numa and normal balancers
> > use the same view of the state of the system.
> >
> > - large arm64system: 2 nodes / 224 CPUs
> > hackbench -l (256000/#grp) -g #grp
> >
> > grp    tip/sched/core         +patchset              improvement
> > 1      14,008(+/- 4,99 %)     13,800(+/- 3.88 %)     1,48 %
> > 4       4,340(+/- 5.35 %)      4.283(+/- 4.85 %)     1,33 %
> > 16      3,357(+/- 0.55 %)      3.359(+/- 0.54 %)    -0,06 %
> > 32      3,050(+/- 0.94 %)      3.039(+/- 1,06 %)     0,38 %
> > 64      2.968(+/- 1,85 %)      3.006(+/- 2.92 %)    -1.27 %
> > 128     3,290(+/-12.61 %)      3,108(+/- 5.97 %)     5.51 %
> > 256     3.235(+/- 3.95 %)      3,188(+/- 2.83 %)     1.45 %
> >
>
> Intuitively the patch makes sense but I'm not a fan of using hackbench
> for evaluating NUMA balancing. The tasks are too short-lived and it's
> not sensitive enough to data placement because of the small footprint
> and because hackbench tends to saturate a machine.
>
> As predicting NUMA balancing behaviour in your head can be difficult, I've
> queued up a battery of tests on a few different NUMA machines and will see
> what falls out. It'll take a few days as some of the tests are long-lived.

Thanks for testing Mel

>
> Baseline will be 5.9-rc2 as I haven't looked at the topology rework in
> tip/sched/core and this patch should not be related to it.

looks fine to me

>
> --
> Mel Gorman
> SUSE Labs