Messages in this thread | | | Date | Mon, 1 Mar 2010 15:53:44 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 20/43] workqueue: reimplement work flushing using linked works |
| |
On 02/26, Tejun Heo wrote: > > +static void move_linked_works(struct work_struct *work, struct list_head *head, > + struct work_struct **nextp) > +{ > ... > + work = list_entry(work->entry.prev, struct work_struct, entry); > + list_for_each_entry_safe_continue(work, n, NULL, entry) {
list_for_each_entry_safe_from(work) ? It doesn't need to move this work back.
> @@ -680,7 +734,27 @@ static int worker_thread(void *__worker) > if (kthread_should_stop()) > break; > > - run_workqueue(worker); > + spin_lock_irq(&cwq->lock); > + > + while (!list_empty(&cwq->worklist)) { > + struct work_struct *work = > + list_first_entry(&cwq->worklist, > + struct work_struct, entry); > + > + if (likely(!(*work_data_bits(work) & > + WORK_STRUCT_LINKED))) { > + /* optimization path, not strictly necessary */ > + process_one_work(worker, work); > + if (unlikely(!list_empty(&worker->scheduled))) > + process_scheduled_works(worker); > + } else { > + move_linked_works(work, &worker->scheduled, > + NULL); > + process_scheduled_works(worker); > + } > + }
So. If the next pending work W doesn't have WORK_STRUCT_LINKED, it will be executed first, then we flush ->scheduled.
But,
> static void insert_wq_barrier(struct cpu_workqueue_struct *cwq, > - struct wq_barrier *barr, struct list_head *head) > + struct wq_barrier *barr, > + struct work_struct *target, struct worker *worker) > { > ... > + /* > + * If @target is currently being executed, schedule the > + * barrier to the worker; otherwise, put it after @target. > + */ > + if (worker) > + head = worker->scheduled.next;
this is the "target == current_work" case,
> - insert_work(cwq, &barr->work, head, work_color_to_flags(WORK_NO_COLOR)); > + insert_work(cwq, &barr->work, head, > + work_color_to_flags(WORK_NO_COLOR) | linked); > }
and in this case we put this barrier at the head of ->scheduled list.
This means, this barrier will run after that work W, not before it?
Hmm. And what if there are no pending works but ->current_work == target ? Again, we add the barrier to ->scheduled, but in this case worker_thread() can't even notice ->scheduled is not empty because it only checks ->worklist?
Well. most probably I just misread this code completely...
insert_wq_barrier() also does:
unsigned long *bits = work_data_bits(target); ... *bits |= WORK_STRUCT_LINKED;
perhaps this needs atomic_long_set(), although I am not sure this really matters.
Oleg.
| |