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

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Date:   Thu, 27 Aug 2020 16:35:34 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/numa: use runnable_avg to classify node

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 %
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>

The testing was a mixed bag of wins and losses but wins more than it
loses. Biggest loss was a 9.04% regression on nas-SP using openmp for
parallelisation on Zen1. Biggest win was around 8% gain running
specjbb2005 on Zen2 (with some major gains of up to 55% for some thread
counts). Most workloads were stable across multiple Intel and AMD
machines.

There were some oddities in changes in NUMA scanning rate but that is
likely a side-effect because the locality over time for the same loads
did not look obviously worse. There was no negative result I could point
at that was not offset by a positive result elsewhere. Given it's not
a univeral win or loss, matching numa and lb balancing as closely as
possible is best so

Reviewed-by: Mel Gorman <mgorman@...e.de>

Thanks.

-- 
Mel Gorman
SUSE Labs