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workqueue: Add system_percpu_wq and system_dfl_wq

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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.

system_wq is a per-CPU worqueue, yet nothing in its name tells about that
CPU affinity constraint, which is very often not required by users. Make it
clear by adding a system_percpu_wq.

system_unbound_wq should be the default workqueue so as not to enforce
locality constraints for random work whenever it's not required.

Adding system_dfl_wq to encourage its use when unbound work should be used.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Marco Crivellari
2025-06-14 15:35:29 +02:00
committed by Tejun Heo
parent 0ff41df1cb
commit 128ea9f6cc
2 changed files with 14 additions and 7 deletions
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8
include/linux/workqueue.h
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@@ -427,7 +427,7 @@ enum wq_consts {
/*
* System-wide workqueues which are always present.
*
* system_wq is the one used by schedule[_delayed]_work[_on]().
* system_percpu_wq is the one used by schedule[_delayed]_work[_on]().
* Multi-CPU multi-threaded. There are users which expect relatively
* short queue flush time. Don't queue works which can run for too
* long.
@@ -438,7 +438,7 @@ enum wq_consts {
* system_long_wq is similar to system_wq but may host long running
* works. Queue flushing might take relatively long.
*
* system_unbound_wq is unbound workqueue. Workers are not bound to
* system_dfl_wq is unbound workqueue. Workers are not bound to
* any specific CPU, not concurrency managed, and all queued works are
* executed immediately as long as max_active limit is not reached and
* resources are available.
@@ -455,10 +455,12 @@ enum wq_consts {
* system_bh[_highpri]_wq are convenience interface to softirq. BH work items
* are executed in the queueing CPU's BH context in the queueing order.
*/
extern struct workqueue_struct *system_wq;
extern struct workqueue_struct *system_wq; /* use system_percpu_wq, this will be removed */
extern struct workqueue_struct *system_percpu_wq;
extern struct workqueue_struct *system_highpri_wq;
extern struct workqueue_struct *system_long_wq;
extern struct workqueue_struct *system_unbound_wq;
extern struct workqueue_struct *system_dfl_wq;
extern struct workqueue_struct *system_freezable_wq;
extern struct workqueue_struct *system_power_efficient_wq;
extern struct workqueue_struct *system_freezable_power_efficient_wq;