RDMA/core: 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]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Leon Romanovsky <[e-mail]>

drivers/infiniband/core/cm.c

···
 	get_random_bytes(&cm.random_id_operand, sizeof cm.random_id_operand);
 	INIT_LIST_HEAD(&cm.timewait_list);
 
-	cm.wq = alloc_workqueue("ib_cm", 0, 1);
+	cm.wq = alloc_workqueue("ib_cm", WQ_PERCPU, 1);
 	if (!cm.wq) {
 		ret = -ENOMEM;
 		goto error2;

drivers/infiniband/core/device.c

···
 {
 	int ret = -ENOMEM;
 
-	ib_wq = alloc_workqueue("infiniband", 0, 0);
+	ib_wq = alloc_workqueue("infiniband", WQ_PERCPU, 0);
 	if (!ib_wq)
 		return -ENOMEM;
 
···
 		goto err;
 
 	ib_comp_wq = alloc_workqueue("ib-comp-wq",
-			WQ_HIGHPRI | WQ_MEM_RECLAIM | WQ_SYSFS, 0);
+			WQ_HIGHPRI | WQ_MEM_RECLAIM | WQ_SYSFS | WQ_PERCPU, 0);
 	if (!ib_comp_wq)
 		goto err_unbound;