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Sender: Tejun Heo <htejun@gmail.com>
Date: Wed, 17 Jan 2024 09:42:31 -1000
From: Tejun Heo <tj@kernel.org>
To: Waiman Long <longman@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Aaron Tomlin <atomlin@atomlin.com>,
	Valentin Schneider <vschneid@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 3/4] kernel/workqueue: Distinguish between general
 unbound and WQ_SYSFS cpumask changes
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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