linux-kernel - [PATCH 5/5] ACPI: thermal: WQ_PERCPU added to alloc

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Message-ID: <20251030154739.262582-6-marco.crivellari@suse.com>
Date: Thu, 30 Oct 2025 16:47:39 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-acpi@...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>,
	Len Brown <lenb@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>
Subject: [PATCH 5/5] ACPI: thermal: WQ_PERCPU added to alloc_workqueue users

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 adds a new WQ_PERCPU flag to explicitly request
alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.

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.

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>
CC: Zhang Rui <rui.zhang@...el.com>
---
 drivers/acpi/thermal.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/thermal.c b/drivers/acpi/thermal.c
index 8537395b417b..a511f9ea0267 100644
--- a/drivers/acpi/thermal.c
+++ b/drivers/acpi/thermal.c
@@ -1060,7 +1060,8 @@ static int __init acpi_thermal_init(void)
 	}

 	acpi_thermal_pm_queue = alloc_workqueue("acpi_thermal_pm",
-						WQ_HIGHPRI | WQ_MEM_RECLAIM, 0);
+						WQ_HIGHPRI | WQ_MEM_RECLAIM | WQ_PERCPU,
+						0);
 	if (!acpi_thermal_pm_queue)
 		return -ENODEV;

-- 
2.51.0