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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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