linux-kernel - Re: [PATCH v4] sched/fair: Introduce SIS_UTIL to search idle CPU based on sum of util

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Date:   Fri, 24 Jun 2022 09:29:58 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     K Prateek Nayak <kprateek.nayak@....com>
Cc:     Chen Yu <yu.c.chen@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Barry Song <21cnbao@...il.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Len Brown <len.brown@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Aubrey Li <aubrey.li@...el.com>,
        Abel Wu <wuyun.abel@...edance.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Tim Chen <tim.c.chen@...el.com>, linux-kernel@...r.kernel.org,
        Yicong Yang <yangyicong@...ilicon.com>,
        Mohini Narkhede <mohini.narkhede@...el.com>
Subject: Re: [PATCH v4] sched/fair: Introduce SIS_UTIL to search idle CPU
 based on sum of util_avg

On Wed, Jun 22, 2022 at 12:06:55PM +0530, K Prateek Nayak wrote:
> Hello Chenyu,
> 
> I'm sorry for the delay. The testing took a while but below are
> the results from testing on our system.
> 
> tl;dr
> 
> o We ran all the tests with with SIS_PROP disabled.
> o tbench reaches close to saturation early with 256 clients.
> o schbench shows improvements for low worker counts.
> o All other benchmark results seem comparable to tip.
>   We don't see any serious regressions with v4.
> 
> > @@ -61,6 +61,7 @@ SCHED_FEAT(TTWU_QUEUE, true)
> >   * When doing wakeups, attempt to limit superfluous scans of the LLC domain.
> >   */
> >  SCHED_FEAT(SIS_PROP, true)
> 
> SIS_PROP was disabled in our testing as follows:
> 
> --
> -SCHED_FEAT(SIS_PROP, true)
> +SCHED_FEAT(SIS_PROP, false)

So how about I make this change.

> With v4 on the current tip, I don't see any need for
> a special case for systems with smaller LLCs with
> SIS_PROP disabled and SIS_UITL enable. Even SIS Efficiency
> seems to be better with SIS_UTIL for hackbench.
> 
> Tested-by: K Prateek Nayak <kprateek.nayak@....com> 

And apply this thing, lets see how it fares..