linux-kernel - Re: [PATCH v3 4/6] sched/fair: Carve out logic to mark a group for asymmetric packing

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Date:   Tue, 18 May 2021 12:18:28 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Len Brown <len.brown@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        Quentin Perret <qperret@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, Aubrey Li <aubrey.li@...el.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v3 4/6] sched/fair: Carve out logic to mark a group for
 asymmetric packing

On Mon, May 17, 2021 at 04:21:36PM +0200, Dietmar Eggemann wrote:
> On 13/05/2021 17:49, Ricardo Neri wrote:
> 
> [...]
> 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index c8c04e9d0d3b..c8b66a5d593e 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -8447,6 +8447,20 @@ group_type group_classify(unsigned int imbalance_pct,
> >  	return group_has_spare;
> >  }
> >  
> > +static inline bool
> > +sched_asym(struct lb_env *env, struct sd_lb_stats *sds,  struct sg_lb_stats *sgs,
> > +	   struct sched_group *group)
> > +{
> > +	/*
> > +	 * Because sd->groups starts with the local group, anything that isn't
> > +	 * the local group will have access to the local state.
> > +	 */
> > +	if (group == sds->local)
> > +		return false;
> 
> sched_asym() is called under if(!local_group ...) from
> update_sg_lb_stats(). So why checking this here again?

This is true. It looks to me that this check is not needed. I makes
sense to me to keep the check in update_sg_lb_stats() so that we can
avoid the extra checks, right?

Thanks and BR,
Ricardo