[PATCH] tracing: Replace use of system_wq with system_percpu_wq

[PATCH] tracing: Replace use of system_wq with system_percpu_wq

[Marco Crivellari]

This patch continues the effort to refactor workqueue APIs, which has begun
with the changes introducing new workqueues and a new alloc_workqueue flag:

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

The point of the refactoring is to eventually alter the default behavior of
workqueues to become unbound by default so that their workload placement is
optimized by the scheduler.

Before that to happen after a careful review and conversion of each individual
case, workqueue users must be converted to the better named new workqueues with
no intended behaviour changes:

   system_wq -> system_percpu_wq
   system_unbound_wq -> system_dfl_wq

This way the old obsolete workqueues (system_wq, system_unbound_wq) can be
removed in the future.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
---
 kernel/trace/trace_events_filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 385af8405392..bb6de1d38f78 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1375,7 +1375,7 @@ static void free_filter_list_tasks(struct rcu_head *rhp)
 	struct filter_head *filter_list = container_of(rhp, struct filter_head, rcu);
 
 	INIT_RCU_WORK(&filter_list->rwork, free_filter_list_work);
-	queue_rcu_work(system_wq, &filter_list->rwork);
+	queue_rcu_work(system_percpu_wq, &filter_list->rwork);
 }
 
 /*
-- 
2.52.0

Re: [PATCH] tracing: Replace use of system_wq with system_percpu_wq

[Steven Rostedt]

On Wed, 24 Dec 2025 17:20:00 +0100
Marco Crivellari <marco.crivellari@suse.com> wrote:

> Before that to happen after a careful review and conversion of each individual
> case, workqueue users must be converted to the better named new workqueues with
> no intended behaviour changes:
> 
>    system_wq -> system_percpu_wq
>    system_unbound_wq -> system_dfl_wq
> 
> This way the old obsolete workqueues (system_wq, system_unbound_wq) can be
> removed in the future.
> 
> Suggested-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
> ---
>  kernel/trace/trace_events_filter.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index 385af8405392..bb6de1d38f78 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -1375,7 +1375,7 @@ static void free_filter_list_tasks(struct rcu_head *rhp)
>  	struct filter_head *filter_list = container_of(rhp, struct filter_head, rcu);
>  
>  	INIT_RCU_WORK(&filter_list->rwork, free_filter_list_work);
> -	queue_rcu_work(system_wq, &filter_list->rwork);
> +	queue_rcu_work(system_percpu_wq, &filter_list->rwork);

This is just garbage collection and has no need to be done on the CPU it
was queued on. I guess this can use system_dfl_wq?

-- Steve


>  }
>  

Re: [PATCH] tracing: Replace use of system_wq with system_percpu_wq

[Marco Crivellari]

Hi Steven,

On Wed, Dec 24, 2025 at 9:43 PM Steven Rostedt <rostedt@goodmis.org> wrote:
> [...]
> > @@ -1375,7 +1375,7 @@ static void free_filter_list_tasks(struct rcu_head *rhp)
> >       struct filter_head *filter_list = container_of(rhp, struct filter_head, rcu);
> >
> >       INIT_RCU_WORK(&filter_list->rwork, free_filter_list_work);
> > -     queue_rcu_work(system_wq, &filter_list->rwork);
> > +     queue_rcu_work(system_percpu_wq, &filter_list->rwork);
>
> This is just garbage collection and has no need to be done on the CPU it
> was queued on. I guess this can use system_dfl_wq?

I will check and I will send a new version with the unbound wq.

Thanks!
-- 

Marco Crivellari

L3 Support Engineer