linux-kernel - Re: [PATCH v4 04/11] sched/fair: rework load

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Date:   Mon, 18 Nov 2019 14:57:05 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        Hillf Danton <hdanton@...a.com>,
        Parth Shah <parth@...ux.ibm.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v4 04/11] sched/fair: rework load_balance

On Mon, 18 Nov 2019 at 14:50, Ingo Molnar <mingo@...nel.org> wrote:
>
>
> * Mel Gorman <mgorman@...hsingularity.net> wrote:
>
> > s/groupe_type/group_type/
> >
> > >  enum group_type {
> > > -   group_other = 0,
> > > +   group_has_spare = 0,
> > > +   group_fully_busy,
> > >     group_misfit_task,
> > > +   group_asym_packing,
> > >     group_imbalanced,
> > > -   group_overloaded,
> > > +   group_overloaded
> > > +};
> > > +
> >
> > While not your fault, it would be nice to comment on the meaning of each
> > group type. From a glance, it's not obvious to me why a misfit task should
> > be a high priority to move a task than a fully_busy (but not overloaded)
> > group given that moving the misfit task might make a group overloaded.
>
> This part of your feedback should now be addressed in the scheduler tree
> via:
>
>   a9723389cc75: sched/fair: Add comments for group_type and balancing at SD_NUMA level
>
> > > +enum migration_type {
> > > +   migrate_load = 0,
> > > +   migrate_util,
> > > +   migrate_task,
> > > +   migrate_misfit
> > >  };
> > >
> >
> > Could do with a comment explaining what migration_type is for because
> > the name is unhelpful. I *think* at a glance it's related to what sort
> > of imbalance is being addressed which is partially addressed by the
> > group_type. That understanding may change as I continue reading the series
> > but now I have to figure it out which means it'll be forgotten again in
> > 6 months.
>
> Agreed. Vincent, is any patch brewing here, or should I take a stab?
>

No I haven't patch under preparation for this
So you can go ahead

Thanks,
Vincent

> Thanks,
>
>         Ingo