Re: [PATCH 4/4] Workqueue: add WQ_PERCPU to every alloc_workqueue user

[Frederic Weisbecker <frederic@kernel.org>]

Le Mon, May 05, 2025 at 11:22:16AM +0200, Michal Hocko a écrit :
> On Sat 03-05-25 10:28:34, Marco Crivellari wrote:
> > By default, alloc_workqueue() creates bound workqueues
> > (i.e., without WQ_UNBOUND).
> > 
> > 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.
> 
> I assume that the next step is to drop WQ_PERCPU when it is not strictly
> necessary, right?

Indeed. And also convert the users of schedule_work() and queue_work(system_wq, ...)

> 
> Looking at the huge list this will be a huge undergoing. Is there any
> rule of thumb to tell whether WQ_PERCPU is required or not? Maybe
> something as simple as - if the worker doesn't use any per cpu variables
> then it is highly likely that it doesn't need WQ_PERCPU? Are there other
> useful hints?

None that I know of. But yes it is a very big work. Ideally we
should focus on core users first. And then we can think about
the drivers later...

-- 
Frederic Weisbecker
SUSE Labs