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

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Message-ID: <20250919153008.324338-2-marco.crivellari@suse.com>
Date: Fri, 19 Sep 2025 17:30:08 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-pm@...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>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Pavel Machek <pavel@...nel.org>,
	Len Brown <len.brown@...el.com>
Subject: [PATCH v2 1/1] PM: WQ_UNBOUND added to pm_wq workqueue

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;
 }
-- 
2.51.0