linux-kernel - Re: [PATCH 3/4] sched/fair: Consider SMT in ASYM

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Message-ID: <20210406231751.GC27195@ranerica-svr.sc.intel.com>
Date:   Tue, 6 Apr 2021 16:17:51 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.comi>, 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>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH 3/4] sched/fair: Consider SMT in ASYM_PACKING load balance

On Tue, Apr 06, 2021 at 01:18:09PM +0200, Peter Zijlstra wrote:
> On Mon, Apr 05, 2021 at 09:11:07PM -0700, Ricardo Neri wrote:
> > +static bool cpu_group_is_smt(int cpu, struct sched_group *sg)
> > +{
> > +#ifdef CONFIG_SCHED_SMT
> > +	if (!static_branch_likely(&sched_smt_present))
> > +		return false;
> > +
> > +	if (sg->group_weight == 1)
> > +		return false;
> > +
> > +	if (cpumask_weight(cpu_smt_mask(cpu)) == 1)
> > +		return false;
> 
> Please explain this condition. Why is it required?

Thank you for your quick review Peter!

Probably this is not required since the previous check verifies the
group weight, and the subsequent check makes sure that @sg matches the
SMT siblings of @cpu.

Thanks and BR,
Ricardo