drivers/block: 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 <[e-mail]>
Signed-off-by: Marco Crivellari <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/aoe/aoemain.c

···
 {
 	int ret;
 
-	aoe_wq = alloc_workqueue("aoe_wq", 0, 0);
+	aoe_wq = alloc_workqueue("aoe_wq", WQ_PERCPU, 0);
 	if (!aoe_wq)
 		return -ENOMEM;
 

drivers/block/rbd.c

···
 	 * The number of active work items is limited by the number of
 	 * rbd devices * queue depth, so leave @max_active at default.
 	 */
-	rbd_wq = alloc_workqueue(RBD_DRV_NAME, WQ_MEM_RECLAIM, 0);
+	rbd_wq = alloc_workqueue(RBD_DRV_NAME, WQ_MEM_RECLAIM | WQ_PERCPU, 0);
 	if (!rbd_wq) {
 		rc = -ENOMEM;
 		goto err_out_slab;

drivers/block/rnbd/rnbd-clt.c

···
 		unregister_blkdev(rnbd_client_major, "rnbd");
 		return err;
 	}
-	rnbd_clt_wq = alloc_workqueue("rnbd_clt_wq", 0, 0);
+	rnbd_clt_wq = alloc_workqueue("rnbd_clt_wq", WQ_PERCPU, 0);
 	if (!rnbd_clt_wq) {
 		pr_err("Failed to load module, alloc_workqueue failed.\n");
 		rnbd_clt_destroy_sysfs_files();

drivers/block/sunvdc.c

···
 {
 	int err;
 
-	sunvdc_wq = alloc_workqueue("sunvdc", 0, 0);
+	sunvdc_wq = alloc_workqueue("sunvdc", WQ_PERCPU, 0);
 	if (!sunvdc_wq)
 		return -ENOMEM;
 

drivers/block/virtio_blk.c

···
 {
 	int error;
 
-	virtblk_wq = alloc_workqueue("virtio-blk", 0, 0);
+	virtblk_wq = alloc_workqueue("virtio-blk", WQ_PERCPU, 0);
 	if (!virtblk_wq)
 		return -ENOMEM;