linux-kernel - [PATCH 4/4] scsi: scsi_transport_fc: WQ_PERCPU added to alloc

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Message-ID: <20251031095643.74246-5-marco.crivellari@suse.com>
Date: Fri, 31 Oct 2025 10:56:43 +0100
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org,
	linux-scsi@...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>,
	"James E . J . Bottomley" <James.Bottomley@...senPartnership.com>,
	"Martin K . Petersen" <martin.petersen@...cle.com>
Subject: [PATCH 4/4] scsi: scsi_transport_fc: 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/scsi/scsi_transport_fc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_transport_fc.c b/drivers/scsi/scsi_transport_fc.c
index 3a821afee9bc..987befb02408 100644
--- a/drivers/scsi/scsi_transport_fc.c
+++ b/drivers/scsi/scsi_transport_fc.c
@@ -441,7 +441,8 @@ static int fc_host_setup(struct transport_container *tc, struct device *dev,
 	fc_host->next_vport_number = 0;
 	fc_host->npiv_vports_inuse = 0;

-	fc_host->work_q = alloc_workqueue("fc_wq_%d", 0, 0, shost->host_no);
+	fc_host->work_q = alloc_workqueue("fc_wq_%d", WQ_PERCPU, 0,
+					  shost->host_no);
 	if (!fc_host->work_q)
 		return -ENOMEM;

@@ -3088,7 +3089,7 @@ fc_remote_port_create(struct Scsi_Host *shost, int channel,

 	spin_unlock_irqrestore(shost->host_lock, flags);

-	rport->devloss_work_q = alloc_workqueue("fc_dl_%d_%d", 0, 0,
+	rport->devloss_work_q = alloc_workqueue("fc_dl_%d_%d", WQ_PERCPU, 0,
 						shost->host_no, rport->number);
 	if (!rport->devloss_work_q) {
 		printk(KERN_ERR "FC Remote Port alloc_workqueue failed\n");
-- 
2.51.0