linux-kernel - Re: [RFC PATCH 0/2] workqueue: Introduce PF_WQ_RESCUE

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Date: Fri, 15 Dec 2023 07:50:46 +0100
From: Juri Lelli <juri.lelli@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: Aaron Tomlin <atomlin@...mlin.com>, linux-kernel@...r.kernel.org,
	jiangshanlai@...il.com, peterz@...radead.org
Subject: Re: [RFC PATCH 0/2] workqueue: Introduce PF_WQ_RESCUE_WORKER

On 14/12/23 09:47, Tejun Heo wrote:
> Hello,
> 
> On Thu, Dec 14, 2023 at 12:25:25PM +0100, Juri Lelli wrote:
> > > So, we have to use set_cpus_allowed_ptr() but we still don't want to change
> > > the affinity of a rescuer which is already running a task for a pool.
> > 
> > But then, even today, a rescuer might keep handling work on a cpu
> > outside its wq cpumask if the associated wq cpumask change can proceed
> > w/o waiting for it to finish the iteration?
> 
> Yeah, that can happen and pool cpumasks naturally being subsets of the wq's
> cpumask that they're serving, your original approach likely isn't broken
> either.
> 
> > BTW, apologies for all the questions, but I'd like to make sure I can
> > get the implications hopefully right. :)
> 
> I obviously haven't thought through it very well, so thanks for the
> questions. So, yeah, I think we actually need to set the rescuer's cpumask
> when wq's cpumask changes and doing it where you were suggesting should
> probably work.

OK. Going to send a proper patch asap.

Thanks!
Juri