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workqueue: WQ_PERCPU added to alloc_workqueue users

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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.

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>
This commit is contained in:
Marco Crivellari 2025-09-14 15:44:26 +02:00 committed by Tejun Heo
parent a2be943b46
commit dadb3ebcf3
2 changed files with 12 additions and 12 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

4
include/linux/workqueue.h
View file

@ -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))

20
kernel/workqueue.c
View file

@ -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 ||