linux-kernel - Re: [PATCH v2] sched/fair: Age the average idle time

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Date:   Wed, 16 Jun 2021 17:52:25 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] sched/fair: Age the average idle time

On Tue, 15 Jun 2021 at 22:43, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Jun 15, 2021 at 12:16:11PM +0100, Mel Gorman wrote:
> > From: Peter Zijlstra (Intel) <peterz@...radead.org>
> >
> > This is a partial forward-port of Peter Ziljstra's work first posted
> > at https://lore.kernel.org/lkml/20180530142236.667774973@infradead.org/.
>
> It's patches 2 and 3 together, right?
>
> > His Signed-off has been removed because it is modified but will be restored
> > if he says it's still ok.
>
> I suppose the SoB will auto-magically re-appear if I apply it :-)
>
> > The patch potentially matters when a socket was multiple LLCs as the
> > maximum search depth is lower. However, some of the test results were
> > suspiciously good (e.g. specjbb2005 gaining 50% on a Zen1 machine) and
> > other results were not dramatically different to other mcahines.
> >
> > Given the nature of the patch, Peter's full series is not being forward
> > ported as each part should stand on its own. Preferably they would be
> > merged at different times to reduce the risk of false bisections.
>
> I'm tempted to give it a go.. anyone object?

Just finished running some tests on my large arm64 system.
Tbench tests are a mixed between small gain and loss

hackbench shows significant changes in both direction
hackbench -g $group

group  tip/sched/core      + this patch
1      13.358(+/- 1.82%)   12.850(+/- 2.21%) +4%
4      4.286(+/- 2.77%)    4.114(+/- 2.25%)  +4%
16     3.175(+/- 0.55%)    3.559(+/- 0.43%)  -12%
32     2.912(+/- 0.79%)    3.165(+/- 0.95%)  -8%
64     2.859(+/- 1.12%)    2.937(+/- 0.91%)  -3%
128    3.092(+/- 4.75%)    3.003(+/-5.18%)   +3%
256    3.233(+/- 3.03%)    2.973(+/- 0.80%)  +8%