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 <[e-mail]>
Signed-off-by: Marco Crivellari <[e-mail]>
Reviewed-by: Justin Tee <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/scsi_transport_fc.c

···
 	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;
 
···
 
 	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");