linux-kernel - Re: [RFC 4/4] sched/fair: Take into runnable

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Message-ID: <CAKfTPtBEUJVxUa8k=-fKXKJwwj4VJv0CAh-2xG0j6Z5vG1xVjA@mail.gmail.com>
Date:   Fri, 14 Feb 2020 08:48:18 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Valentin Schneider <valentin.schneider@....com>
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>, Mel Gorman <mgorman@...e.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Phil Auld <pauld@...hat.com>, Parth Shah <parth@...ux.ibm.com>
Subject: Re: [RFC 4/4] sched/fair: Take into runnable_avg to classify group

On Thu, 13 Feb 2020 at 19:37, Valentin Schneider
<valentin.schneider@....com> wrote:
>
> On 2/13/20 6:32 PM, Valentin Schneider wrote:
> >> @@ -7911,6 +7912,10 @@ group_has_capacity(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
> >>      if (sgs->sum_nr_running < sgs->group_weight)
> >>              return true;
> >>
> >> +    if ((sgs->group_capacity * imbalance_pct) <
> >> +                    (sgs->group_runnable * 100))
> >> +            return false;
> >> +
> >
> > I haven't stared long enough at patch 2, but I'll ask anyway - with this new
> > condition, do we still need the next one (based on util)? AIUI
> > group_runnable is >= group_util, so if group_runnable is within the allowed
> > margin then group_util has to be as well.
> >
>
> Hmph, actually util_est breaks the runnable >= util assumption I think...

yes, that's 1 reason

and also the 2 conditions are a bit different as  the imbalance_pct is
not on the same side of the condition.

For util_avg, the tests is true when util_avg is still below but close
to capacity
For runnable_avg, the test is true  when runnable is significantly
above capacity

>
> >>      if ((sgs->group_capacity * 100) >
> >>                      (sgs->group_util * imbalance_pct))
> >>              return true;