linux-kernel - Re: [PATCH 8/8] sched_ext: idle: Introduce node-aware idle cpu kfunc helpers

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Message-ID: <Z7IY3yr1VErsryqw@slm.duckdns.org>
Date: Sun, 16 Feb 2025 06:57:03 -1000
From: Tejun Heo <tj@...nel.org>
To: Andrea Righi <arighi@...dia.com>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	Yury Norov <yury.norov@...il.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 8/8] sched_ext: idle: Introduce node-aware idle cpu kfunc
 helpers

Hello,

On Fri, Feb 14, 2025 at 08:40:07PM +0100, Andrea Righi wrote:
...
>  const struct cpumask *scx_bpf_get_idle_cpumask_node(int node)
>  const struct cpumask *scx_bpf_get_idle_smtmask_node(int node)
>  s32 scx_bpf_pick_idle_cpu_in_node(const cpumask_t *cpus_allowed,
>  				   int node, u64 flags)

All other functions have just _node as the suffix. Might as well do the same
here?

>  s32 scx_bpf_pick_any_cpu_node(const cpumask_t *cpus_allowed,
>  			       int node, u64 flags)

...
> +__bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask_node(int node)
> +{
> +	node = validate_node(node);
> +	if (node < 0)
> +		return cpu_none_mask;
> +
> +#ifdef CONFIG_SMP
> +	return idle_cpumask(node)->cpu;
> +#else
> +	return cpu_none_mask;

Shouldn't the UP case forwarded to scx_bpf_get_idle_cpumask()? Wouldn't a
NUMA aware scheduler running on a UP kernel end up specifying 0 to these
calls?

> +__bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask_node(int node)
> +{
> +	node = validate_node(node);
> +	if (node < 0)
> +		return cpu_none_mask;
> +
> +#ifdef CONFIG_SMP
> +	if (sched_smt_active())
> +		return idle_cpumask(node)->smt;
> +	else
> +		return idle_cpumask(node)->cpu;
> +#else
> +	return cpu_none_mask;

Ditto here.

Thanks.

-- 
tejun