[PATCH 0/2] add WQ_PERCPU to alloc_workqueue

[PATCH 0/2] add WQ_PERCPU to alloc_workqueue

[Marco Crivellari]

Hi,

=== Current situation: problems ===

Let's consider a nohz_full system with isolated CPUs: wq_unbound_cpumask is
set to the housekeeping CPUs, for !WQ_UNBOUND the local CPU is selected.

This leads to different scenarios if a work item is scheduled on an
isolated CPU where "delay" value is 0 or greater then 0:
        schedule_delayed_work(, 0);

This will be handled by __queue_work() that will queue the work item on the
current local (isolated) CPU, while:

        schedule_delayed_work(, 1);

Will move the timer on an housekeeping CPU, and schedule the work there.

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 consistency cannot be addressed without refactoring the API.

=== Recent changes to the WQ API ===

The following, address the recent changes in the Workqueue API:

- commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
- commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")

The old workqueues will be removed in a future release cycle.

=== Introduced Changes by this series ===

1) [P 1-2] add WQ_PERCPU to alloc_workqueue()

    This change adds a new WQ_PERCPU flag to explicitly request
    alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.


Thanks!


Marco Crivellari (2):
  ath6kl: add WQ_PERCPU to alloc_workqueue users
  cw1200: add WQ_PERCPU to alloc_workqueue users

 drivers/net/wireless/ath/ath6kl/usb.c | 2 +-
 drivers/net/wireless/st/cw1200/bh.c   | 5 +++--
 2 files changed, 4 insertions(+), 3 deletions(-)

-- 
2.51.1

[PATCH 1/2] ath6kl: add WQ_PERCPU to alloc_workqueue users

[Marco Crivellari]

Currently if a user enqueues 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 consistency cannot be addressed without refactoring the API.
For more details see the Link tag below.

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 continues the effort to refactor workqueue APIs, which began with
the introduction of new workqueues and a new alloc_workqueue flag in:

commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")

This change adds a new WQ_PERCPU flag to explicitly request
alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.

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.

Once migration is complete, WQ_UNBOUND can be removed and unbound will
become the implicit default.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
---
 drivers/net/wireless/ath/ath6kl/usb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ath6kl/usb.c b/drivers/net/wireless/ath/ath6kl/usb.c
index 38bb501fc553..bfb21725d779 100644
--- a/drivers/net/wireless/ath/ath6kl/usb.c
+++ b/drivers/net/wireless/ath/ath6kl/usb.c
@@ -637,7 +637,7 @@ static struct ath6kl_usb *ath6kl_usb_create(struct usb_interface *interface)
 	ar_usb = kzalloc(sizeof(struct ath6kl_usb), GFP_KERNEL);
 	if (ar_usb == NULL)
 		return NULL;
-	ar_usb->wq = alloc_workqueue("ath6kl_wq", 0, 0);
+	ar_usb->wq = alloc_workqueue("ath6kl_wq", WQ_PERCPU, 0);
 	if (!ar_usb->wq) {
 		kfree(ar_usb);
 		return NULL;
-- 
2.51.1

[PATCH 2/2] cw1200: add WQ_PERCPU to alloc_workqueue users

[Marco Crivellari]

Currently if a user enqueues 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 consistency cannot be addressed without refactoring the API.
For more details see the Link tag below.

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 continues the effort to refactor workqueue APIs, which began with
the introduction of new workqueues and a new alloc_workqueue flag in:

commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")

This change adds a new WQ_PERCPU flag to explicitly request
alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.

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.

Once migration is complete, WQ_UNBOUND can be removed and unbound will
become the implicit default.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
---
 drivers/net/wireless/st/cw1200/bh.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/st/cw1200/bh.c b/drivers/net/wireless/st/cw1200/bh.c
index 3b4ded2ac801..bdf7132c5849 100644
--- a/drivers/net/wireless/st/cw1200/bh.c
+++ b/drivers/net/wireless/st/cw1200/bh.c
@@ -54,8 +54,9 @@ int cw1200_register_bh(struct cw1200_common *priv)
 	int err = 0;
 	/* Realtime workqueue */
 	priv->bh_workqueue = alloc_workqueue("cw1200_bh",
-				WQ_MEM_RECLAIM | WQ_HIGHPRI
-				| WQ_CPU_INTENSIVE, 1);
+				WQ_MEM_RECLAIM | WQ_HIGHPRI |
+				WQ_CPU_INTENSIVE | WQ_PERCPU,
+				1);
 
 	if (!priv->bh_workqueue)
 		return -ENOMEM;
-- 
2.51.1

Re: [PATCH 1/2] ath6kl: add WQ_PERCPU to alloc_workqueue users

[Marco Crivellari]

On Thu, Nov 13, 2025 at 5:12 PM Marco Crivellari
<marco.crivellari@suse.com> wrote:
>
> Currently if a user enqueues 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 consistency cannot be addressed without refactoring the API.
> For more details see the Link tag below.
>
> 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 continues the effort to refactor workqueue APIs, which began with
> the introduction of new workqueues and a new alloc_workqueue flag in:
>
> commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
>
> This change adds a new WQ_PERCPU flag to explicitly request
> alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.
>
> 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.
>
> Once migration is complete, WQ_UNBOUND can be removed and unbound will
> become the implicit default.
>
> Suggested-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
> Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
> ---
>  drivers/net/wireless/ath/ath6kl/usb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/ath/ath6kl/usb.c b/drivers/net/wireless/ath/ath6kl/usb.c
> index 38bb501fc553..bfb21725d779 100644
> --- a/drivers/net/wireless/ath/ath6kl/usb.c
> +++ b/drivers/net/wireless/ath/ath6kl/usb.c
> @@ -637,7 +637,7 @@ static struct ath6kl_usb *ath6kl_usb_create(struct usb_interface *interface)
>         ar_usb = kzalloc(sizeof(struct ath6kl_usb), GFP_KERNEL);
>         if (ar_usb == NULL)
>                 return NULL;
> -       ar_usb->wq = alloc_workqueue("ath6kl_wq", 0, 0);
> +       ar_usb->wq = alloc_workqueue("ath6kl_wq", WQ_PERCPU, 0);
>         if (!ar_usb->wq) {
>                 kfree(ar_usb);
>                 return NULL;

[ Cc-ing Andrew Morton ]

Hello Andrew,

This file is orphaned. Can you help me in order to have this patch merged?

Thank you!

-- 

Marco Crivellari

L3 Support Engineer

Re: [PATCH 1/2] ath6kl: add WQ_PERCPU to alloc_workqueue users

[Frederic Weisbecker]

Le Thu, Mar 05, 2026 at 05:44:04PM +0100, Marco Crivellari a écrit :
> On Thu, Nov 13, 2025 at 5:12 PM Marco Crivellari
> <marco.crivellari@suse.com> wrote:
> >
> > Currently if a user enqueues 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 consistency cannot be addressed without refactoring the API.
> > For more details see the Link tag below.
> >
> > 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 continues the effort to refactor workqueue APIs, which began with
> > the introduction of new workqueues and a new alloc_workqueue flag in:
> >
> > commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> > commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
> >
> > This change adds a new WQ_PERCPU flag to explicitly request
> > alloc_workqueue() to be per-cpu when WQ_UNBOUND has not been specified.
> >
> > 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.
> >
> > Once migration is complete, WQ_UNBOUND can be removed and unbound will
> > become the implicit default.
> >
> > Suggested-by: Tejun Heo <tj@kernel.org>
> > Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
> > Link: https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/
> > ---
> >  drivers/net/wireless/ath/ath6kl/usb.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/wireless/ath/ath6kl/usb.c b/drivers/net/wireless/ath/ath6kl/usb.c
> > index 38bb501fc553..bfb21725d779 100644
> > --- a/drivers/net/wireless/ath/ath6kl/usb.c
> > +++ b/drivers/net/wireless/ath/ath6kl/usb.c
> > @@ -637,7 +637,7 @@ static struct ath6kl_usb *ath6kl_usb_create(struct usb_interface *interface)
> >         ar_usb = kzalloc(sizeof(struct ath6kl_usb), GFP_KERNEL);
> >         if (ar_usb == NULL)
> >                 return NULL;
> > -       ar_usb->wq = alloc_workqueue("ath6kl_wq", 0, 0);
> > +       ar_usb->wq = alloc_workqueue("ath6kl_wq", WQ_PERCPU, 0);
> >         if (!ar_usb->wq) {
> >                 kfree(ar_usb);
> >                 return NULL;
> 
> [ Cc-ing Andrew Morton ]
> 
> Hello Andrew,
> 
> This file is orphaned. Can you help me in order to have this patch merged?
> 
> Thank you!
>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

-- 
Frederic Weisbecker
SUSE Labs