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.

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 the WQ_UNBOUND flag to explicitly request
alloc_workqueue() to be unbound, because this specific workload has no
benefit being per-cpu.

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>
---
Changes in v2:
- This workload benefit from an unbound workqueue. So change WQ_PERCPU
  with WQ_UNBOUND_WQ.

- Rebased on 6.18-rc5
---
 drivers/firewire/core-transaction.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/firewire/core-transaction.c b/drivers/firewire/core-transaction.c
index c65f491c54d0..a9677a8affb7 100644
--- a/drivers/firewire/core-transaction.c
+++ b/drivers/firewire/core-transaction.c
@@ -1437,7 +1437,8 @@ static int __init fw_core_init(void)
 {
 	int ret;
 
-	fw_workqueue = alloc_workqueue("firewire", WQ_MEM_RECLAIM, 0);
+	fw_workqueue = alloc_workqueue("firewire", WQ_MEM_RECLAIM | WQ_UNBOUND,
+				       0);
 	if (!fw_workqueue)
 		return -ENOMEM;
 
-- 
2.51.1

Hi,

On Wed, Nov 12, 2025 at 01:01:25PM +0100, Marco Crivellari 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.
> 
> 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 the WQ_UNBOUND flag to explicitly request
> alloc_workqueue() to be unbound, because this specific workload has no
> benefit being per-cpu.
> 
> 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>
> ---
> Changes in v2:
> - This workload benefit from an unbound workqueue. So change WQ_PERCPU
>   with WQ_UNBOUND_WQ.
> 
> - Rebased on 6.18-rc5
> ---
>  drivers/firewire/core-transaction.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Applied to for-next branch.

I'm sorry not to reply to your previous post since it did not reach my
mail box... Your v2 patch is a good reminder ;)


Thanks

Takashi Sakamoto

On Wed, Nov 12, 2025 at 1:56 PM Takashi Sakamoto
<o-takashi@sakamocchi.jp> wrote:
> [...]
> Applied to for-next branch.
>
> I'm sorry not to reply to your previous post since it did not reach my
> mail box... Your v2 patch is a good reminder ;)
>

Thank you!
No problem Takashi! :-)

-- 

Marco Crivellari

L3 Support Engineer, Technology & Product