workqueue: 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 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: Tejun Heo <tj@kernel.org>

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index b6834b7aee4bce98fc5d93170bd7031c4dd813dc..71a9900c03c706070d44b35bd7f45aead4b37d75 100644 (file)
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -410,7 +410,7 @@ enum wq_flags {
        __WQ_LEGACY             = 1 << 18, /* internal: create*_workqueue() */
 
        /* BH wq only allows the following flags */
-       __WQ_BH_ALLOWS          = WQ_BH | WQ_HIGHPRI,
+       __WQ_BH_ALLOWS          = WQ_BH | WQ_HIGHPRI | WQ_PERCPU,
 };
 
 enum wq_consts {
@@ -570,7 +570,7 @@ alloc_workqueue_lockdep_map(const char *fmt, unsigned int flags, int max_active,
        alloc_workqueue(fmt, WQ_UNBOUND | __WQ_ORDERED | (flags), 1, ##args)
 
 #define create_workqueue(name)                                         \
-       alloc_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM, 1, (name))
+       alloc_workqueue("%s", __WQ_LEGACY | WQ_MEM_RECLAIM | WQ_PERCPU, 1, (name))
 #define create_freezable_workqueue(name)                               \
        alloc_workqueue("%s", __WQ_LEGACY | WQ_FREEZABLE | WQ_UNBOUND | \
                        WQ_MEM_RECLAIM, 1, (name))

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 90db8cf015c2fbafef1137850037f1a2eb5087bd..45320e27a16c4a5a6c7642388f445ad4b86a8f27 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -7828,22 +7828,22 @@ void __init workqueue_init_early(void)
                ordered_wq_attrs[i] = attrs;
        }
 
-       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_wq = alloc_workqueue("events", WQ_PERCPU, 0);
+       system_percpu_wq = alloc_workqueue("events", WQ_PERCPU, 0);
+       system_highpri_wq = alloc_workqueue("events_highpri",
+                                           WQ_HIGHPRI | WQ_PERCPU, 0);
+       system_long_wq = alloc_workqueue("events_long", WQ_PERCPU, 0);
        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);
+                                             WQ_FREEZABLE | WQ_PERCPU, 0);
        system_power_efficient_wq = alloc_workqueue("events_power_efficient",
-                                             WQ_POWER_EFFICIENT, 0);
+                                             WQ_POWER_EFFICIENT | WQ_PERCPU, 0);
        system_freezable_power_efficient_wq = alloc_workqueue("events_freezable_pwr_efficient",
-                                             WQ_FREEZABLE | WQ_POWER_EFFICIENT,
-                                             0);
-       system_bh_wq = alloc_workqueue("events_bh", WQ_BH, 0);
+                                             WQ_FREEZABLE | WQ_POWER_EFFICIENT | WQ_PERCPU, 0);
+       system_bh_wq = alloc_workqueue("events_bh", WQ_BH | WQ_PERCPU, 0);
        system_bh_highpri_wq = alloc_workqueue("events_bh_highpri",
-                                              WQ_BH | WQ_HIGHPRI, 0);
+                                              WQ_BH | WQ_HIGHPRI | WQ_PERCPU, 0);
        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 ||