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

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Message-ID: <Zagtpw-JQvdpFseh@slm.duckdns.org>
Date: Wed, 17 Jan 2024 09:42:31 -1000
From: Tejun Heo <tj@...nel.org>
To: Waiman Long <longman@...hat.com>
Cc: Juri Lelli <juri.lelli@...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

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.

-- 
tejun