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Message-ID: <20250614133531.76742-2-marco.crivellari@suse.com>
Date: Sat, 14 Jun 2025 15:35:29 +0200
From: Marco Crivellari <marco.crivellari@...e.com>
To: linux-kernel@...r.kernel.org
Cc: Tejun Heo <tj@...nel.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
Frederic Weisbecker <frederic@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Marco Crivellari <marco.crivellari@...e.com>,
Michal Hocko <mhocko@...e.com>
Subject: [PATCH v5 1/3] Workqueue: add system_percpu_wq and system_dfl_wq
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@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
include/linux/workqueue.h | 8 +++++---
kernel/workqueue.c | 13 +++++++++----
2 files changed, 14 insertions(+), 7 deletions(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 6e30f275da77..502ec4a5e32c 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -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;
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 97f37b5bae66..9047f658ccf2 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -505,12 +505,16 @@ static struct kthread_worker *pwq_release_worker __ro_after_init;
struct workqueue_struct *system_wq __ro_after_init;
EXPORT_SYMBOL(system_wq);
+struct workqueue_struct *system_percpu_wq __ro_after_init;
+EXPORT_SYMBOL(system_percpu_wq);
struct workqueue_struct *system_highpri_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_highpri_wq);
struct workqueue_struct *system_long_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_long_wq);
struct workqueue_struct *system_unbound_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_unbound_wq);
+struct workqueue_struct *system_dfl_wq __ro_after_init;
+EXPORT_SYMBOL_GPL(system_dfl_wq);
struct workqueue_struct *system_freezable_wq __ro_after_init;
EXPORT_SYMBOL_GPL(system_freezable_wq);
struct workqueue_struct *system_power_efficient_wq __ro_after_init;
@@ -7829,10 +7833,11 @@ void __init workqueue_init_early(void)
}
system_wq = alloc_workqueue("events", 0, 0);
+ system_percpu_wq = alloc_workqueue("events", 0, 0);
system_highpri_wq = alloc_workqueue("events_highpri", WQ_HIGHPRI, 0);
system_long_wq = alloc_workqueue("events_long", 0, 0);
- system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
- WQ_MAX_ACTIVE);
+ system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND, WQ_MAX_ACTIVE);
+ system_dfl_wq = alloc_workqueue("events_unbound", WQ_UNBOUND, WQ_MAX_ACTIVE);
system_freezable_wq = alloc_workqueue("events_freezable",
WQ_FREEZABLE, 0);
system_power_efficient_wq = alloc_workqueue("events_power_efficient",
@@ -7843,8 +7848,8 @@ void __init workqueue_init_early(void)
system_bh_wq = alloc_workqueue("events_bh", WQ_BH, 0);
system_bh_highpri_wq = alloc_workqueue("events_bh_highpri",
WQ_BH | WQ_HIGHPRI, 0);
- BUG_ON(!system_wq || !system_highpri_wq || !system_long_wq ||
- !system_unbound_wq || !system_freezable_wq ||
+ BUG_ON(!system_wq || !system_percpu_wq|| !system_highpri_wq || !system_long_wq ||
+ !system_unbound_wq || !system_freezable_wq || !system_dfl_wq ||
!system_power_efficient_wq ||
!system_freezable_power_efficient_wq ||
!system_bh_wq || !system_bh_highpri_wq);
--
2.49.0
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