linux-kernel - [PATCH 3/5] ACPI: EC: WQ_PERCPU added to alloc

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Message-ID: <20251030154739.262582-4-marco.crivellari@suse.com>
Date: Thu, 30 Oct 2025 16:47:37 +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>
Subject: [PATCH 3/5] ACPI: EC: 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>
---
 drivers/acpi/ec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index 7855bbf752b1..59b3d50ff01e 100644
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -2294,7 +2294,8 @@ static int acpi_ec_init_workqueues(void)
 		ec_wq = alloc_ordered_workqueue("kec", 0);

 	if (!ec_query_wq)
-		ec_query_wq = alloc_workqueue("kec_query", 0, ec_max_queries);
+		ec_query_wq = alloc_workqueue("kec_query", WQ_PERCPU,
+					      ec_max_queries);

 	if (!ec_wq || !ec_query_wq) {
 		acpi_ec_destroy_workqueues();
-- 
2.51.0