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@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index b0dc957c3e56024468bee708e853aaf5e2cbf531..74b0042709cd18cf8c2592f7c4ae197e8cf11317 100644 (file)
--- 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 cf620328273757e4e9a06f8f29ca7ead436db47b..71a4dd59977c8e005c0a50c36b5a716cdd3636da 100644 (file)
--- 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;
@@ -7816,10 +7820,11 @@ 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",
@@ -7830,8 +7835,8 @@ 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);