linux-kernel - Re: [PATCH v4 07/24] sched/fair: Compute IPC class scores for load balancing

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Message-ID: <20230706234850.GD12259@ranerica-svr.sc.intel.com>
Date:   Thu, 6 Jul 2023 16:48:50 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Ionela Voinescu <ionela.voinescu@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ricardo Neri <ricardo.neri@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Valentin Schneider <vschneid@...hat.com>,
        Lukasz Luba <lukasz.luba@....com>,
        Zhao Liu <zhao1.liu@...el.com>,
        "Yuan, Perry" <Perry.Yuan@....com>, x86@...nel.org,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        "Tim C . Chen" <tim.c.chen@...el.com>,
        Zhao Liu <zhao1.liu@...ux.intel.com>
Subject: Re: [PATCH v4 07/24] sched/fair: Compute IPC class scores for load
 balancing

On Mon, Jun 26, 2023 at 02:01:25PM -0700, Tim Chen wrote:
> On Sun, 2023-06-25 at 13:11 -0700, Ricardo Neri wrote:
> > 
> > > > +
> > > > +	score_on_dst_cpu = arch_get_ipcc_score(sgs->min_ipcc, env->dst_cpu);
> > > > +
> > > > +	/*
> > > > +	 * Do not use IPC scores. sgs::ipcc_score_{after, before} will be zero
> > > > +	 * and not used.
> > > > +	 */
> 
> The comment is not matching the check below.  If zero
> is not used, the check should also reflect the case.

Agreed. This comment is not clear. I meant to say that returning here
has the effect of leaving the `before` and `after` scores of this group as
zero.

Since zero is the minimum possible score, this group will not be selected
during the tie breaker, unless the statistics of all other groups are also
zero.

> 
> > > > +	if (IS_ERR_VALUE(score_on_dst_cpu))
> > > > +		return;
> > > > +
> > > > +	before = sgs->sum_score;
> > > > +	after = before - sgs->min_score;
> > > 
> > 
> Tim