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

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Date:   Thu, 14 Dec 2023 12:25:25 +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 13/12/23 08:38, Tejun Heo wrote:
> On Wed, Dec 13, 2023 at 07:32:10PM +0100, Juri Lelli wrote:
> > > Maybe the easiest way to do this is making rescuer_thread() restore the wq's
> > > cpumask right before going to sleep, and making apply_wqattrs_commit() just
> > > wake up the rescuer.
> > 
> > Hummm, don't think we can call that either while the rescuer is actually
> > running. Maybe we can simply s/kthread_bind_mask/set_cpus_allowed_ptr/
> > in the above?
> 
> 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?

BTW, apologies for all the questions, but I'd like to make sure I can
get the implications hopefully right. :)

Thanks,
Juri