linux-kernel - [PATCH 2/2] power: supply: WQ_PERCPU added to alloc

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Message-ID: <20250905090641.106297-3-marco.crivellari@suse.com>
Date: Fri,  5 Sep 2025 11:06:41 +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>,
	Sebastian Reichel <sre@...nel.org>
Subject: [PATCH 2/2] power: supply: 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 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 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>
---
 drivers/power/supply/ab8500_btemp.c       | 3 ++-
 drivers/power/supply/ipaq_micro_battery.c | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/power/supply/ab8500_btemp.c b/drivers/power/supply/ab8500_btemp.c
index b00c84fbc33c..e5202a7b6209 100644
--- a/drivers/power/supply/ab8500_btemp.c
+++ b/drivers/power/supply/ab8500_btemp.c
@@ -667,7 +667,8 @@ static int ab8500_btemp_bind(struct device *dev, struct device *master,

 	/* Create a work queue for the btemp */
 	di->btemp_wq =
-		alloc_workqueue("ab8500_btemp_wq", WQ_MEM_RECLAIM, 0);
+		alloc_workqueue("ab8500_btemp_wq", WQ_MEM_RECLAIM | WQ_PERCPU,
+				0);
 	if (di->btemp_wq == NULL) {
 		dev_err(dev, "failed to create work queue\n");
 		return -ENOMEM;
diff --git a/drivers/power/supply/ipaq_micro_battery.c b/drivers/power/supply/ipaq_micro_battery.c
index 7e0568a5353f..ff8573a5ca6d 100644
--- a/drivers/power/supply/ipaq_micro_battery.c
+++ b/drivers/power/supply/ipaq_micro_battery.c
@@ -232,7 +232,8 @@ static int micro_batt_probe(struct platform_device *pdev)
 		return -ENOMEM;

 	mb->micro = dev_get_drvdata(pdev->dev.parent);
-	mb->wq = alloc_workqueue("ipaq-battery-wq", WQ_MEM_RECLAIM, 0);
+	mb->wq = alloc_workqueue("ipaq-battery-wq",
+				 WQ_MEM_RECLAIM | WQ_PERCPU, 0);
 	if (!mb->wq)
 		return -ENOMEM;

-- 
2.51.0