linux-kernel - Re: [PATCH 3/6] sched_ext: Introduce per-node idle cpumasks

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Message-ID: <Z2L1vxl2ZAe_SleS@gpd3>
Date: Wed, 18 Dec 2024 17:18:07 +0100
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>
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>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] sched_ext: Introduce per-node idle cpumasks

On Wed, Dec 18, 2024 at 06:10:17AM -1000, Tejun Heo wrote:
> Hello,
> 
> On Wed, Dec 18, 2024 at 11:21:30AM +0100, Andrea Righi wrote:
> ...
> > > Are node IDs guaranteed to be consecutive? Shouldn't it be `node >=
> > > nr_node_ids`? Also, should probably add node_possible(node)?
> > 
> > Or even better add node_online(node), an offline NUMA node shouldn't be
> > used in this context.
> 
> That can be too but then we'd have to worry about synchronizing against
> going on/offline. Looks like that's protected by mem_hotplug_lock, so we'd
> have to require get_online_mems() around these iterations, which might not
> be worth it. Besides, if we want to triger abort on incorrect input, we'd
> have to call sched_ext ops under mem_hotplug_lock, which we probably can't
> do.

We can probably ignore this for now and add a "restart" logic like we do
with CPU hotplugging at some point.

-Andrea