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

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Date:   Mon, 13 Jun 2022 16:06:36 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     Yicong Yang <yangyicong@...wei.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Mel Gorman <mgorman@...e.de>, yangyicong@...ilicon.com,
        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,
        K Prateek Nayak <kprateek.nayak@....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 Mon, Jun 13, 2022 at 03:40:52PM +0800, Yicong Yang wrote:
> On 2022/6/13 0:34, Chen Yu wrote:
> >  
[cut...]
> >  #define NUMA_IMBALANCE_MIN 2
> > diff --git a/kernel/sched/features.h b/kernel/sched/features.h
> > index 1cf435bbcd9c..3334a1b93fc6 100644
> > --- a/kernel/sched/features.h
> > +++ b/kernel/sched/features.h
> > @@ -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)
> > +SCHED_FEAT(SIS_UTIL, true)
> >  
> 
> confused here that shouldn't we have SCHED_FEAT(SIS_PROP, false)? With SIS_UTIL enabled, SIS_PROP will have no
> effect since nr is overridden by SIS_UTIL.
Yes, no matter what SIS_PROP is set, the result of SIS_UTIL would be used to decide
the scan depth. We don't change the default value of SIS_PROP here, as this patch
tends to only touch one feature at one time. And the options could be tuned by user via
sysfs manually. Besides, the target is to replace SIS_PROP with another search policy,
Peter mentioned that "And ideally we're remove SIS_PROP after a few releases if this
works out", so I assume that changing the default value of SIS_PROP does not matter
in current patch.

thanks,
Chenyu