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Date: Thu, 15 Dec 2011 16:38:12 +0100
From: Johannes Berg <johannes@...solutions.net>
To: Tejun Heo <tj@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: workqueue_set_max_active(wq, 0)?
Hi Tejun,
> > Before I dive in more deeply I figured I'd ask if you think what a good
> > way of doing this would be (and whether I'm completely insane) :-)
>
> Hmmm... yeah, actually, that's what wq uses internally to implement
> freezable workqueues. It sets max_active to 0 temporarily and waits
> for all in-flight works to finish. On thaw, the original value is
> restored.
>
> Updating workqueue_set_max_active() to return the old value would be a
> nice API update which goes together, I think.
So I looked at set_max_active() but I think it can also be called in
atomic contexts but I would want this to wait I think ... Does the below
look like a reasonable first cut (never mind that it's not really
exported in header files yet, I haven't even tested it yet but the
interaction with other code is interesting)
johannes
---
kernel/workqueue.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 66 insertions(+), 2 deletions(-)
--- a/kernel/workqueue.c 2011-12-10 17:32:26.000000000 +0100
+++ b/kernel/workqueue.c 2011-12-15 16:36:06.000000000 +0100
@@ -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,
/* worker flags */
WORKER_STARTED = 1 << 0, /* started */
@@ -246,6 +247,7 @@ struct workqueue_struct {
#ifdef CONFIG_LOCKDEP
struct lockdep_map lockdep_map;
#endif
+ wait_queue_head_t waitq;
};
struct workqueue_struct *system_wq __read_mostly;
@@ -1759,6 +1761,8 @@ static void cwq_dec_nr_in_flight(struct
if (cwq->nr_active < cwq->max_active)
cwq_activate_first_delayed(cwq);
}
+ if (cwq->nr_active == 0 && cwq->max_active == 0)
+ wake_up(&cwq->wq->waitq);
}
/* is flush in progress and are we at the flushing tip? */
@@ -2990,6 +2994,7 @@ struct workqueue_struct *__alloc_workque
atomic_set(&wq->nr_cwqs_to_flush, 0);
INIT_LIST_HEAD(&wq->flusher_queue);
INIT_LIST_HEAD(&wq->flusher_overflow);
+ init_waitqueue_head(&wq->waitq);
wq->name = name;
lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
@@ -3124,7 +3129,7 @@ void workqueue_set_max_active(struct wor
spin_lock_irq(&gcwq->lock);
if (!(wq->flags & WQ_FREEZABLE) ||
- !(gcwq->flags & GCWQ_FREEZING))
+ !(gcwq->flags & (GCWQ_FREEZING | GCWQ_PAUSING)))
get_cwq(gcwq->cpu, wq)->max_active = max_active;
spin_unlock_irq(&gcwq->lock);
@@ -3377,7 +3382,7 @@ static int __cpuinit trustee_thread(void
* completion while frozen.
*/
while (gcwq->nr_workers != gcwq->nr_idle ||
- gcwq->flags & GCWQ_FREEZING ||
+ gcwq->flags & (GCWQ_FREEZING | GCWQ_PAUSING) ||
gcwq->trustee_state == TRUSTEE_IN_CHARGE) {
int nr_works = 0;
@@ -3767,6 +3772,65 @@ out_unlock:
}
#endif /* CONFIG_FREEZER */
+static unsigned int count_active(struct workqueue_struct *wq)
+{
+ unsigned int cpu, active = 0;
+
+ 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);
+ active += cwq->nr_active;
+ spin_unlock_irq(&gcwq->lock);
+ }
+
+ return active;
+}
+
+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);
+
+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);
+
static int __init init_workqueues(void)
{
unsigned int cpu;
--
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