linux-kernel - [PATCH 1/3] drivers/block: replace use of system_wq with system_percpu

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Message-ID: <20250905085141.93357-2-marco.crivellari@suse.com>
Date: Fri,  5 Sep 2025 10:51:39 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-block@...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>,
	Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 1/3] drivers/block: replace use of system_wq with system_percpu_wq

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.

system_unbound_wq should be the default workqueue so as not to enforce
locality constraints for random work whenever it's not required.

Adding system_dfl_wq to encourage its use when unbound work should be used.

queue_work() / queue_delayed_work() / mod_delayed_work() will now use the
new unbound wq: whether the user still use the old wq a warn will be
printed along with a wq redirect to the new one.

The old system_unbound_wq will be kept for a few release cycles.

Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
 drivers/block/nbd.c    | 2 +-
 drivers/block/sunvdc.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 7bdc7eb808ea..7738fce177fa 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -311,7 +311,7 @@ static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
 		if (args) {
 			INIT_WORK(&args->work, nbd_dead_link_work);
 			args->index = nbd->index;
-			queue_work(system_wq, &args->work);
+			queue_work(system_percpu_wq, &args->work);
 		}
 	}
 	if (!nsock->dead) {
diff --git a/drivers/block/sunvdc.c b/drivers/block/sunvdc.c
index b5727dea15bd..442546b05df8 100644
--- a/drivers/block/sunvdc.c
+++ b/drivers/block/sunvdc.c
@@ -1187,7 +1187,7 @@ static void vdc_ldc_reset(struct vdc_port *port)
 	}

 	if (port->ldc_timeout)
-		mod_delayed_work(system_wq, &port->ldc_reset_timer_work,
+		mod_delayed_work(system_percpu_wq, &port->ldc_reset_timer_work,
 			  round_jiffies(jiffies + HZ * port->ldc_timeout));
 	mod_timer(&port->vio.timer, round_jiffies(jiffies + HZ));
 	return;
-- 
2.51.0