linux-kernel - Re: [PATCH V1 RESEND]: sched/fair: Revise comment about lb decision matrix

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Date:   Fri, 15 Apr 2022 18:03:05 +0800
From:   Tao Zhou <tao.zhou@...ux.dev>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        Tao Zhou <tao.zhou@...ux.dev>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        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>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH V1 RESEND]: sched/fair: Revise comment about lb decision
 matrix

On Fri, Apr 15, 2022 at 10:32:09AM +0200,
Vincent Guittot wrote:

> On Fri, 15 Apr 2022 at 04:22, Tao Zhou <tao.zhou@...ux.dev> wrote:
> >
> > If busiest group type is group_misfit_task, the local
> > group type must be group_has_spare according to below
> > code in update_sd_pick_busiest():
> >
> > if (sgs->group_type == group_misfit_task &&
> >     (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) ||
> >      sds->local_stat.group_type != group_has_spare))
> >          return false;
> >
> > group type imbalanced and overloaded and fully_busy are filtered in here.
> > misfit and asym are filtered before in update_sg_lb_stats().
> 
> The behavior has changed with
> cad68e552e77 ("sched/fair: Consider misfit tasks when load-balancing")
> But we haven't updated the matrix
> 
> Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>

I send a version just now but forget to change the version number.

Thanks,
Tao

> > So, change the decision matrix to:
> >
> > busiest \ local has_spare fully_busy misfit asym imbalanced overloaded
> > has_spare        nr_idle   balanced   N/A    N/A  balanced   balanced
> > fully_busy       nr_idle   nr_idle    N/A    N/A  balanced   balanced
> > misfit_task      force     N/A        N/A    N/A  *N/A*      *N/A*
> > asym_packing     force     force      N/A    N/A  force      force
> > imbalanced       force     force      N/A    N/A  force      force
> > overloaded       force     force      N/A    N/A  force      avg_load
> >
> > Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()")
> > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
> > Signed-off-by: Tao Zhou <tao.zhou@...ux.dev>
> > ---
> >
> > v1 changelog:
> > (1) Send to MAINTAINERS/REVIEWS get from `./scripts/get_maintainer.pl`
> >     suggested by Dietmar Eggemann.
> > (2) Based on v5.18-rc2
> >
> >
> >  kernel/sched/fair.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index d4bd299d67ab..b8c67e7c8cf3 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -9495,7 +9495,7 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
> >   * busiest \ local has_spare fully_busy misfit asym imbalanced overloaded
> >   * has_spare        nr_idle   balanced   N/A    N/A  balanced   balanced
> >   * fully_busy       nr_idle   nr_idle    N/A    N/A  balanced   balanced
> > - * misfit_task      force     N/A        N/A    N/A  force      force
> > + * misfit_task      force     N/A        N/A    N/A  N/A        N/A
> >   * asym_packing     force     force      N/A    N/A  force      force
> >   * imbalanced       force     force      N/A    N/A  force      force
> >   * overloaded       force     force      N/A    N/A  force      avg_load
> > --
> > 2.35.2
> >