On Fri, Nov 07, 2025 at 02:27:12PM +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 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 <[email protected]>
> Signed-off-by: Marco Crivellari <[email protected]>
Applied to hyperv-next. Thanks.
I modified the subject prefix to "mshv" and added a new line in the
commit message body to separate the first two paragraphs while at it.
Wei
> ---
> drivers/hv/mshv_eventfd.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hv/mshv_eventfd.c b/drivers/hv/mshv_eventfd.c
> index 806674722868..2a80af1d610a 100644
> --- a/drivers/hv/mshv_eventfd.c
> +++ b/drivers/hv/mshv_eventfd.c
> @@ -592,7 +592,7 @@ static void mshv_irqfd_release(struct mshv_partition *pt)
>
> int mshv_irqfd_wq_init(void)
> {
> - irqfd_cleanup_wq = alloc_workqueue("mshv-irqfd-cleanup", 0, 0);
> + irqfd_cleanup_wq = alloc_workqueue("mshv-irqfd-cleanup", WQ_PERCPU, 0);
> if (!irqfd_cleanup_wq)
> return -ENOMEM;
>
> --
> 2.51.1
>
