linux-kernel - Re: [PATCH v2 1/1] PM: WQ_UNBOUND added to pm

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Message-ID: <CAJZ5v0hvTogN-egwXWRp3F1iJ0HS_eSJ4hEavjrMuKF5RVxuHQ@mail.gmail.com>
Date: Mon, 13 Oct 2025 20:51:28 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Marco Crivellari <marco.crivellari@...e.com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	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>, "Rafael J . Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@...nel.org>, 
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH v2 1/1] PM: WQ_UNBOUND added to pm_wq workqueue

On Fri, Sep 19, 2025 at 5:30 PM Marco Crivellari
<marco.crivellari@...e.com> 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 change add the WQ_UNBOUND flag to pm_wq, to make explicit this
> workqueue can be unbound and that it does not benefit from per-cpu work.
>
> Once migration is complete, WQ_UNBOUND can be removed and unbound will
> become the implicit default.
>
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
> ---
>  kernel/power/main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/power/main.c b/kernel/power/main.c
> index 3cf2d7e72567..33a47ed15994 100644
> --- a/kernel/power/main.c
> +++ b/kernel/power/main.c
> @@ -1056,7 +1056,7 @@ EXPORT_SYMBOL_GPL(pm_wq);
>
>  static int __init pm_start_workqueue(void)
>  {
> -       pm_wq = alloc_workqueue("pm", WQ_FREEZABLE, 0);
> +       pm_wq = alloc_workqueue("pm", WQ_FREEZABLE | WQ_UNBOUND, 0);
>
>         return pm_wq ? 0 : -ENOMEM;
>  }
> --

Applied as 6.19 material, thanks!