Received-SPF: pass (google.com: domain of linux-kernel+bounces-30118-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Date: Thu, 18 Jan 2024 13:52:57 +0100
From: Juri Lelli <juri.lelli@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: Waiman Long <longman@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
Message-ID: <ZakfKWVdAUZ4wCNf@localhost.localdomain>
References: <20240116161929.232885-1-juri.lelli@redhat.com>
 <20240116161929.232885-4-juri.lelli@redhat.com>
 <ZabRlEklmuqwFPj-@slm.duckdns.org>
 <ZafQwMw8ZKztunMU@localhost.localdomain>
 <ZagKbRlBxZHsKiw5@mtj.duckdns.org>
 <72e4a971-96e5-44b7-b348-bbdb68e54b40@redhat.com>
 <Zagtpw-JQvdpFseh@slm.duckdns.org>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Zagtpw-JQvdpFseh@slm.duckdns.org>

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