linux-kernel - Re: [PATCH v2 4/7] sched/fair: Introduce sched_smt_siblings

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Date:   Mon, 12 Dec 2022 09:54:58 -0800
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     "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>,
        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>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [PATCH v2 4/7] sched/fair: Introduce sched_smt_siblings_idle()

On Tue, Dec 06, 2022 at 07:03:37PM +0100, Dietmar Eggemann wrote:
> On 22/11/2022 21:35, Ricardo Neri wrote:
> > Architectures that implement arch_asym_cpu_priority() may need to know the
> > idle state of the SMT siblings of a CPU. The scheduler has this information
> > and functionality. Expose it.
> > 
> > Move the existing functionality outside of the NUMA code.
> 
> [...]
> 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 0e4251f83807..9517c48df50e 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -1052,6 +1052,28 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >   * Scheduling class queueing methods:
> >   */
> >  
> > +static inline bool is_core_idle(int cpu)
> > +{
> > +#ifdef CONFIG_SCHED_SMT
> > +	int sibling;
> > +
> > +	for_each_cpu(sibling, cpu_smt_mask(cpu)) {
> > +		if (cpu == sibling)
> > +			continue;
> > +
> > +		if (!idle_cpu(sibling))
> > +			return false;
> > +	}
> > +#endif
> > +
> > +	return true;
> > +}
> > +
> > +bool sched_smt_siblings_idle(int cpu)
> > +{
> > +	return is_core_idle(cpu);
> > +}
> 
> Nitpick: Can we not just have one exported function for both use-cases:
> NUMA and x86 ITMT?

By adding a new function I intend to preserve the inlinig of is_core_idle()
in update_numa_stats() (via numa_idle_core(), which is also inline). Do you
think there is no value?

A downside of having the new function is that now the code is duplicated
in update_numa_stats() and sched_smt_siblings_idle().

I can take your suggestion if losing the inline is OK.

Thanks and BR,
Ricardo