Commit d7b1cdc9 authored Sep 05, 2025 by Marco Crivellari Committed by Jens Axboe Sep 09, 2025

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 <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 456cefcb

drivers/block/aoe/aoemain.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -44,7 +44,7 @@ aoe_init(void)
		{
		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

+1 −1

Original line number	Diff line number	Diff line
		@@ -7389,7 +7389,7 @@ static int __init rbd_init(void)
		* 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

+1 −1

Original line number	Diff line number	Diff line
		@@ -1809,7 +1809,7 @@ static int __init rnbd_client_init(void)
		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

+1 −1

Original line number	Diff line number	Diff line
		@@ -1216,7 +1216,7 @@ static int __init vdc_init(void)
		{
		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

+1 −1

Original line number	Diff line number	Diff line
		@@ -1682,7 +1682,7 @@ static int __init virtio_blk_init(void)
		{
		int error;

		virtblk_wq = alloc_workqueue("virtio-blk", 0, 0);
		virtblk_wq = alloc_workqueue("virtio-blk", WQ_PERCPU, 0);
		if (!virtblk_wq)
		return -ENOMEM;