linux-kernel - Re: [RFC PATCH 3/4] kernel/workqueue: Distinguish between general unbound and WQ

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Message-ID: <ZakfKWVdAUZ4wCNf@localhost.localdomain>
Date: Thu, 18 Jan 2024 13:52:57 +0100
From: Juri Lelli <juri.lelli@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: Waiman Long <longman@...hat.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Aaron Tomlin <atomlin@...mlin.com>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/4] kernel/workqueue: Distinguish between general
 unbound and WQ_SYSFS cpumask changes

On 17/01/24 09:42, Tejun Heo wrote:
> Hello,
> 
> On Wed, Jan 17, 2024 at 02:32:34PM -0500, Waiman Long wrote:
> > My impression is that changing the workqueue cpumask of ordered unbound
> > workqueue may break the ordering guarantee momentarily. I was planning to
> 
> Ah, you're right. Changing cpumask would require changing the dfl_pwq and
> that can introduce extra concurrency and break ordering and it's exempt from
> unbound_cpumask updates. We likely need to add a mechanism for updating
> ordered wq's so that the new pwq doesn't become until the previous one is
> drained.

Thanks for the additional info! Guess I'll need to think more about this
and possibly coordinate the effort with Waiman.

Best,
Juri