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 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>
---
include/linux/workqueue.h | 4 ++--
kernel/workqueue.c | 19 ++++++++++---------
2 files changed, 12 insertions(+), 11 deletions(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 542529d3b41b..4db59f886656 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -409,7 +409,7 @@ 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 {
@@ -568,7 +568,7 @@ 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 89839eebb359..d33ca6acc5a5 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -7819,22 +7819,23 @@ 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);
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, 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_dfl_wq || !system_freezable_wq ||
!system_power_efficient_wq ||
--
2.51.0
Hello,
The patch doesn't apply to wq/for-6.18 and...
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 89839eebb359..d33ca6acc5a5 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -7819,22 +7819,23 @@ 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);
> 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, 0);
Isn't this missing WQ_PERCPU for system_freezable_power_efficient_wq?
Thanks.
--
tejun
On Fri, Sep 5, 2025 at 7:25 PM Tejun Heo <tj@kernel.org> wrote: > Isn't this missing WQ_PERCPU for system_freezable_power_efficient_wq? I guess the flag is also missing for system_power_efficient_wq, because by default it should be per-cpu, unless there is wq_power_efficient=true. -- Marco Crivellari L3 Support Engineer, Technology & Product marco.crivellari@suse.com
On Fri, Sep 5, 2025 at 7:25 PM Tejun Heo <tj@kernel.org> wrote:
>
> Hello,
>
> The patch doesn't apply to wq/for-6.18 and...
Hello Tejun,
I will rebase the work.
> > system_freezable_power_efficient_wq = alloc_workqueue("events_freezable_pwr_efficient",
> > - WQ_FREEZABLE | WQ_POWER_EFFICIENT,
> > - 0);
>
> Isn't this missing WQ_PERCPU for system_freezable_power_efficient_wq?
Yes, you're right. Sorry for that.
I will send the v2.
Thanks a lot!
--
Marco Crivellari
L3 Support Engineer, Technology & Product
marco.crivellari@suse.com
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