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SubjectRe: workqueue_set_max_active(wq, 0)?
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Hi,

> > @@ -51,6 +51,7 @@ enum {
> > GCWQ_DISASSOCIATED = 1 << 2, /* cpu can't serve workers */
> > GCWQ_FREEZING = 1 << 3, /* freeze in progress */
> > GCWQ_HIGHPRI_PENDING = 1 << 4, /* highpri works on queue */
> > + GCWQ_PAUSING = 1 << 5,
>
> Hmmm... confused. Pausing is per-wq, why is this flag on gcwq?
> Shouldn't it be on workqueue_struct?

Hm, no idea :-)
I just copied FREEZING really without knowing what I was doing. I'm not
very familiar with this code (yet).

> > +void pause_workqueue(struct workqueue_struct *wq)
> > +{
> > + unsigned int cpu;
> > +
> > + for_each_cwq_cpu(cpu, wq) {
> > + struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
> > + struct global_cwq *gcwq = cwq->gcwq;
> > +
> > + spin_lock_irq(&gcwq->lock);
> > +
> > + WARN_ON(gcwq->flags & GCWQ_PAUSING);
> > + gcwq->flags |= GCWQ_PAUSING;
> > +
> > + cwq->max_active = 0;
> > +
> > + spin_unlock_irq(&gcwq->lock);
> > + }
> > +
> > + wait_event(wq->waitq, count_active(wq) == 0);
> > +}
> > +EXPORT_SYMBOL(pause_workqueue);
>
> What if there are multiple callers of this function on the same wq?
> Maybe something like wq->pause_depth and also use it from freeze path?

Hm, good point. We can't abstract out all of it -- the freezer API
doesn't want to wait for it to finish -- but probably a bit of it.

How do you iterate workqueues? We'd have to do that for the freezer
part, unless we want to work on CWQs again.

Actually I'm not really sure I understand the differences between WQ,
CWQ and GCWQ...

> > +void resume_workqueue(struct workqueue_struct *wq)
> > +{
> > + unsigned int cpu;
> > +
> > + for_each_cwq_cpu(cpu, wq) {
> > + struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
> > + struct global_cwq *gcwq = cwq->gcwq;
> > +
> > + spin_lock_irq(&gcwq->lock);
> > +
> > + WARN_ON(!(gcwq->flags & GCWQ_PAUSING));
> > + gcwq->flags &= ~GCWQ_PAUSING;
> > +
> > + cwq->max_active = wq->saved_max_active;
> > +
> > + wake_up_worker(gcwq);
> > + spin_unlock_irq(&gcwq->lock);
> > + }
> > +}
> > +EXPORT_SYMBOL(resume_workqueue);
>
> I don't think wake_up_worker() would be sufficient.
> cwq_activate_first_delayed() needs to be called to kick the delayed
> work items.

Hm, ok.

> I think it would be great if this can be abstracted out so that both
> the freezer and explicit pausing use the same facility. They aren't
> that different after all.

I'll take a look tomorrow. If you want to beat me to it ... ;-)

johannes



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