linux-kernel - [PATCH 2/3] workqueue: replace use of system_wq with system_percpu

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Message-ID: <20250905091325.112168-3-marco.crivellari@suse.com>
Date: Fri,  5 Sep 2025 11:13:24 +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>,
	Frederic Weisbecker <frederic@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>
Subject: [PATCH 2/3] workqueue: replace use of system_wq with system_percpu_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.

queue_work() / queue_delayed_work() mod_delayed_work() will now use the
new per-cpu wq: whether the user still stick on the old name a warn will
be printed along a wq redirect to the new one.

This patch add the new system_percpu_wq except for mm, fs and net
subsystem, whom are handled in separated patches.

The old wq will be kept for a few release cylces.

Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
---
 include/linux/workqueue.h | 22 +++++++++++-----------
 kernel/workqueue.c        |  2 +-
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 0e14d78fb970..542529d3b41b 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -433,10 +433,10 @@ enum wq_consts {
  * short queue flush time.  Don't queue works which can run for too
  * long.
  *
- * system_highpri_wq is similar to system_wq but for work items which
+ * system_highpri_wq is similar to system_percpu_wq but for work items which
  * require WQ_HIGHPRI.
  *
- * system_long_wq is similar to system_wq but may host long running
+ * system_long_wq is similar to system_percpu_wq but may host long running
  * works.  Queue flushing might take relatively long.
  *
  * system_dfl_wq is unbound workqueue.  Workers are not bound to
@@ -444,13 +444,13 @@ enum wq_consts {
  * executed immediately as long as max_active limit is not reached and
  * resources are available.
  *
- * system_freezable_wq is equivalent to system_wq except that it's
+ * system_freezable_wq is equivalent to system_percpu_wq except that it's
  * freezable.
  *
  * *_power_efficient_wq are inclined towards saving power and converted
  * into WQ_UNBOUND variants if 'wq_power_efficient' is enabled; otherwise,
  * they are same as their non-power-efficient counterparts - e.g.
- * system_power_efficient_wq is identical to system_wq if
+ * system_power_efficient_wq is identical to system_percpu_wq if
  * 'wq_power_efficient' is disabled.  See WQ_POWER_EFFICIENT for more info.
  *
  * system_bh[_highpri]_wq are convenience interface to softirq. BH work items
@@ -704,7 +704,7 @@ static inline bool mod_delayed_work(struct workqueue_struct *wq,
  */
 static inline bool schedule_work_on(int cpu, struct work_struct *work)
 {
-	return queue_work_on(cpu, system_wq, work);
+	return queue_work_on(cpu, system_percpu_wq, work);
 }
 
 /**
@@ -723,7 +723,7 @@ static inline bool schedule_work_on(int cpu, struct work_struct *work)
  */
 static inline bool schedule_work(struct work_struct *work)
 {
-	return queue_work(system_wq, work);
+	return queue_work(system_percpu_wq, work);
 }
 
 /**
@@ -766,15 +766,15 @@ extern void __warn_flushing_systemwide_wq(void)
 #define flush_scheduled_work()						\
 ({									\
 	__warn_flushing_systemwide_wq();				\
-	__flush_workqueue(system_wq);					\
+	__flush_workqueue(system_percpu_wq);					\
 })
 
 #define flush_workqueue(wq)						\
 ({									\
 	struct workqueue_struct *_wq = (wq);				\
 									\
-	if ((__builtin_constant_p(_wq == system_wq) &&			\
-	     _wq == system_wq) ||					\
+	if ((__builtin_constant_p(_wq == system_percpu_wq) &&			\
+	     _wq == system_percpu_wq) ||					\
 	    (__builtin_constant_p(_wq == system_highpri_wq) &&		\
 	     _wq == system_highpri_wq) ||				\
 	    (__builtin_constant_p(_wq == system_long_wq) &&		\
@@ -803,7 +803,7 @@ extern void __warn_flushing_systemwide_wq(void)
 static inline bool schedule_delayed_work_on(int cpu, struct delayed_work *dwork,
 					    unsigned long delay)
 {
-	return queue_delayed_work_on(cpu, system_wq, dwork, delay);
+	return queue_delayed_work_on(cpu, system_percpu_wq, dwork, delay);
 }
 
 /**
@@ -817,7 +817,7 @@ static inline bool schedule_delayed_work_on(int cpu, struct delayed_work *dwork,
 static inline bool schedule_delayed_work(struct delayed_work *dwork,
 					 unsigned long delay)
 {
-	return queue_delayed_work(system_wq, dwork, delay);
+	return queue_delayed_work(system_percpu_wq, dwork, delay);
 }
 
 #ifndef CONFIG_SMP
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 687285701655..89839eebb359 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -7660,7 +7660,7 @@ static int wq_watchdog_param_set_thresh(const char *val,
 	if (ret)
 		return ret;
 
-	if (system_wq)
+	if (system_percpu_wq)
 		wq_watchdog_set_thresh(thresh);
 	else
 		wq_watchdog_thresh = thresh;
-- 
2.51.0