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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>
This commit is contained in:
Marco Crivellari 2025-09-05 10:51:41 +02:00 committed by Jens Axboe
parent 456cefcb31
commit d7b1cdc910
5 changed files with 5 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/block/aoe/aoemain.c
View File

@ -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;

2
drivers/block/rbd.c
View File

@ -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;

2
drivers/block/rnbd/rnbd-clt.c
View File

@ -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();

2
drivers/block/sunvdc.c
View File

@ -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;

2
drivers/block/virtio_blk.c
View File

@ -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;