linux-kernel - Re: [PATCH 5/7] sched_ext: idle: Introduce SCX_OPS_BUILTIN_IDLE_PER

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Message-ID: <Z64cO6Y-aWUT07vN@gpd3>
Date: Thu, 13 Feb 2025 17:22:19 +0100
From: Andrea Righi <arighi@...dia.com>
To: Yury Norov <yury.norov@...il.com>
Cc: Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.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.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Joel Fernandes <joel@...lfernandes.org>, Ian May <ianm@...dia.com>,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] sched_ext: idle: Introduce
 SCX_OPS_BUILTIN_IDLE_PER_NODE

On Thu, Feb 13, 2025 at 11:08:01AM -0500, Yury Norov wrote:
...
> > @@ -237,13 +240,19 @@ void scx_idle_update_selcpu_topology(void)
> >  	 * If all CPUs belong to the same NUMA node and the same LLC domain,
> >  	 * enabling both NUMA and LLC optimizations is unnecessary, as checking
> >  	 * for an idle CPU in the same domain twice is redundant.
> > +	 *
> > +	 * If SCX_OPS_BUILTIN_IDLE_PER_NODE is enabled ignore the NUMA
> > +	 * optimization, as we would naturally select idle CPUs within
> > +	 * specific NUMA nodes querying the corresponding per-node cpumask.
> >  	 */
> > -	nr_cpus = numa_weight(cpu);
> > -	if (nr_cpus > 0) {
> > -		if (nr_cpus < num_online_cpus() && llc_numa_mismatch())
> > -			enable_numa = true;
> > -		pr_debug("sched_ext: NUMA=%*pb weight=%u\n",
> > -			 cpumask_pr_args(numa_span(cpu)), numa_weight(cpu));
> > +	if (!(ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)) {
> > +		nr_cpus = numa_weight(cpu);
> > +		if (nr_cpus > 0) {
> > +			if (nr_cpus < num_online_cpus() && llc_numa_mismatch())
> > +				enable_numa = true;
> > +			pr_debug("sched_ext: NUMA=%*pb weight=%u\n",
> > +				 cpumask_pr_args(numa_span(cpu)), numa_weight(cpu));
> 
> No need to call numa_weight(cpu) for the 2nd time, right?

Ah good catch, will fix that.

Thanks,
-Andrea