linux-kernel - Re: [PATCH 5/6] sched_ext: idle: Per-node idle cpumasks

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Message-ID: <Z6r9H6JukZi19dQP@gpd3>
Date: Tue, 11 Feb 2025 08:32:47 +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>, Ian May <ianm@...dia.com>,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] sched_ext: idle: Per-node idle cpumasks

On Mon, Feb 10, 2025 at 11:57:42AM -0500, Yury Norov wrote:
...
> > > +/*
> > > + * Find the best idle CPU in the system, relative to @node.
> > > + */
> > > +s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, int node, u64 flags)
> > > +{
> > > +	nodemask_t unvisited = NODE_MASK_ALL;
> 
> This should be a NODEMASK_ALLOC(). We don't want to eat up too much of the
> stack, right?

Ok, and if I want to initialize unvisited to all online nodes, is there a
better than doing:

  nodemask_clear(*unvisited);
  nodemask_or(*unvisited, *unvisited, node_states[N_ONLINE]);

We don't have nodemask_copy() right?

Thanks,
-Andrea