linux-kernel - Re: [PATCH net-next 3/3] net: WQ_PERCPU added to alloc

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Message-ID: <86200ee5-c0dc-4a70-823a-ae36b2e6c544@redhat.com>
Date: Thu, 11 Sep 2025 11:25:27 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Marco Crivellari <marco.crivellari@...e.com>,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Cc: Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Michal Hocko <mhocko@...e.com>, "David S . Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next 3/3] net: WQ_PERCPU added to alloc_workqueue
 users

On 9/5/25 11:05 AM, Marco Crivellari wrote:
> Currently if a user enqueue a work item using schedule_delayed_work() the
> used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
> WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
> schedule_work() that is using system_wq and queue_work(), that makes use
> again of WORK_CPU_UNBOUND.
> This lack of consistentcy cannot be addressed without refactoring the API.
> 
> alloc_workqueue() treats all queues as per-CPU by default, while unbound
> workqueues must opt-in via WQ_UNBOUND.
> 
> This default is suboptimal: most workloads benefit from unbound queues,
> allowing the scheduler to place worker threads where they’re needed and
> reducing noise when CPUs are isolated.
> 
> This patch adds a new WQ_PERCPU flag at the network subsystem, to explicitly
> request the use of the per-CPU behavior. Both flags coexist for one release
> cycle to allow callers to transition their calls.
> 
> Once migration is complete, WQ_UNBOUND can be removed and unbound will
> become the implicit default.
> 
> With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
> any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
> must now use WQ_PERCPU.
> 
> All existing users have been updated accordingly.
> 
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>

This and patch 1/3 do not apply cleanly to the net-next tree.

Please rebase and repost.

Also I suggest to split the wireless bit out of this series and send
them to the relevant sub tree, to avoid later merge issue.

Thanks,

Paolo