[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] WQ_PERCPU added 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):
  wifi: rtlwifi: add WQ_PERCPU to alloc_workqueue users
  wifi: rtw88: add WQ_PERCPU to alloc_workqueue users

 drivers/net/wireless/realtek/rtlwifi/base.c | 2 +-
 drivers/net/wireless/realtek/rtw88/usb.c    | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

-- 
2.51.1

[PATCH 1/2] wifi: rtlwifi: 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/realtek/rtlwifi/base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/realtek/rtlwifi/base.c b/drivers/net/wireless/realtek/rtlwifi/base.c
index e26feb8de658..2786e4ee67eb 100644
--- a/drivers/net/wireless/realtek/rtlwifi/base.c
+++ b/drivers/net/wireless/realtek/rtlwifi/base.c
@@ -445,7 +445,7 @@ static int _rtl_init_deferred_work(struct ieee80211_hw *hw)
 	struct rtl_priv *rtlpriv = rtl_priv(hw);
 	struct workqueue_struct *wq;
 
-	wq = alloc_workqueue("%s", 0, 0, rtlpriv->cfg->name);
+	wq = alloc_workqueue("%s", WQ_PERCPU, 0, rtlpriv->cfg->name);
 	if (!wq)
 		return -ENOMEM;
 
-- 
2.51.1

[PATCH 2/2] wifi: rtw88: 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/realtek/rtw88/usb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/realtek/rtw88/usb.c b/drivers/net/wireless/realtek/rtw88/usb.c
index 3b5126ffc81a..db60e142268d 100644
--- a/drivers/net/wireless/realtek/rtw88/usb.c
+++ b/drivers/net/wireless/realtek/rtw88/usb.c
@@ -965,7 +965,8 @@ static int rtw_usb_init_rx(struct rtw_dev *rtwdev)
 	struct sk_buff *rx_skb;
 	int i;
 
-	rtwusb->rxwq = alloc_workqueue("rtw88_usb: rx wq", WQ_BH, 0);
+	rtwusb->rxwq = alloc_workqueue("rtw88_usb: rx wq", WQ_BH | WQ_PERCPU,
+				       0);
 	if (!rtwusb->rxwq) {
 		rtw_err(rtwdev, "failed to create RX work queue\n");
 		return -ENOMEM;
-- 
2.51.1

RE: [PATCH 1/2] wifi: rtlwifi: add WQ_PERCPU to alloc_workqueue users

[Ping-Ke Shih]

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/realtek/rtlwifi/base.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/realtek/rtlwifi/base.c b/drivers/net/wireless/realtek/rtlwifi/base.c
> index e26feb8de658..2786e4ee67eb 100644
> --- a/drivers/net/wireless/realtek/rtlwifi/base.c
> +++ b/drivers/net/wireless/realtek/rtlwifi/base.c
> @@ -445,7 +445,7 @@ static int _rtl_init_deferred_work(struct ieee80211_hw *hw)
>         struct rtl_priv *rtlpriv = rtl_priv(hw);
>         struct workqueue_struct *wq;
> 
> -       wq = alloc_workqueue("%s", 0, 0, rtlpriv->cfg->name);
> +       wq = alloc_workqueue("%s", WQ_PERCPU, 0, rtlpriv->cfg->name);

I think this driver should use WQ_UNBOUND as well as another patch in this
patchset. 


I feel most user scenarios should be WQ_UNBOUND. Could you share which case
uses WQ_PERCPU?


>         if (!wq)
>                 return -ENOMEM;
> 
> --
> 2.51.1

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

[Marco Crivellari]

Hi,

On Mon, Nov 17, 2025 at 1:53 AM Ping-Ke Shih <pkshih@realtek.com> wrote:
> [...]
>
> I think this driver should use WQ_UNBOUND as well as another patch in this
> patchset.
>
>
> I feel most user scenarios should be WQ_UNBOUND. Could you share which case
> uses WQ_PERCPU?

I think a typical scenario is when per-cpu variables are used.
But this is not the case here, for both the patches.

So yes, unless there is the need to have the item scheduled on the same CPU,
this can be converted to WQ_UNBOUND.

I did the same for other series in other subsystems. If you want, I
can send the v2
with the change.

Thanks!
--

Marco Crivellari

L3 Support Engineer, Technology & Product

RE: [PATCH 1/2] wifi: rtlwifi: add WQ_PERCPU to alloc_workqueue users

[Ping-Ke Shih]

Marco Crivellari <marco.crivellari@suse.com> wrote:
> Hi,
> 
> On Mon, Nov 17, 2025 at 1:53 AM Ping-Ke Shih <pkshih@realtek.com> wrote:
> > [...]
> >
> > I think this driver should use WQ_UNBOUND as well as another patch in this
> > patchset.
> >
> >
> > I feel most user scenarios should be WQ_UNBOUND. Could you share which case
> > uses WQ_PERCPU?
> 
> I think a typical scenario is when per-cpu variables are used.
> But this is not the case here, for both the patches.
> 
> So yes, unless there is the need to have the item scheduled on the same CPU,
> this can be converted to WQ_UNBOUND.
> 
> I did the same for other series in other subsystems. If you want, I
> can send the v2
> with the change.

Please send v2 with WQ_UNBOUND. Thanks.

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

[Marco Crivellari]

On Tue, Nov 18, 2025 at 1:41 AM Ping-Ke Shih <pkshih@realtek.com> wrote:
> [...]
> Please send v2 with WQ_UNBOUND. Thanks.

Sure, I will do it.

Thanks!


-- 

Marco Crivellari

L3 Support Engineer, Technology & Product

Re: [PATCH 2/2] wifi: rtw88: add WQ_PERCPU to alloc_workqueue users

[Ping-Ke Shih]

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/

1 patch(es) applied to rtw-next branch of rtw.git, thanks.

f65ca6c51179 wifi: rtw88: add WQ_PERCPU to alloc_workqueue users

---
https://github.com/pkshih/rtw.git

Re: [PATCH 2/2] wifi: rtw88: add WQ_PERCPU to alloc_workqueue users

[Marco Crivellari]

On Thu, Jan 22, 2026 at 2:29 AM Ping-Ke Shih <pkshih@realtek.com> wrote:
> [...]
> 1 patch(es) applied to rtw-next branch of rtw.git, thanks.
>
> f65ca6c51179 wifi: rtw88: add WQ_PERCPU to alloc_workqueue users
>

Many thanks!


-- 

Marco Crivellari

L3 Support Engineer