On Fri, Sep 05, 2025 at 11:08:56AM +0200, Marco Crivellari wrote:
> 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.
A duplicate paragraph.
> 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@xxxxxxxxxx>
> Signed-off-by: Marco Crivellari <marco.crivellari@xxxxxxxx>
> ---
> drivers/s390/char/tape_3590.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/s390/char/tape_3590.c b/drivers/s390/char/tape_3590.c
> index 0d484fe43d7e..aee11fece701 100644
> --- a/drivers/s390/char/tape_3590.c
> +++ b/drivers/s390/char/tape_3590.c
> @@ -1670,7 +1670,7 @@ tape_3590_init(void)
>
> DBF_EVENT(3, "3590 init\n");
>
> - tape_3590_wq = alloc_workqueue("tape_3590", 0, 0);
> + tape_3590_wq = alloc_workqueue("tape_3590", WQ_PERCPU, 0);
> if (!tape_3590_wq)
> return -ENOMEM;
Acked-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Thanks!
