drbd: reduce lock contention in drbd_worker

The worker may now dequeue work items in batches.
This should reduce lock contention during busy periods.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 3ed2d871272e13aa786dd69f112b604315490d97..d2d1f97511bd1fe03496834dea3503f2aacdb617 100644 (file)
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -2026,8 +2026,6 @@ static void wait_for_work(struct drbd_connection *connection, struct list_head *
                prepare_to_wait(&connection->sender_work.q_wait, &wait, TASK_INTERRUPTIBLE);
                spin_lock_irq(&connection->resource->req_lock);
                spin_lock(&connection->sender_work.q_lock);     /* FIXME get rid of this one? */
-               /* dequeue single item only,
-                * we still use drbd_queue_work_front() in some places */
                if (!list_empty(&connection->sender_work.q))
                        list_splice_tail_init(&connection->sender_work.q, work_list);
                spin_unlock(&connection->sender_work.q_lock);   /* FIXME get rid of this one? */
@@ -2114,7 +2112,7 @@ int drbd_worker(struct drbd_thread *thi)
                if (get_t_state(thi) != RUNNING)
                        break;
 
-               while (!list_empty(&work_list)) {
+               if (!list_empty(&work_list)) {
                        w = list_first_entry(&work_list, struct drbd_work, list);
                        list_del_init(&w->list);
                        update_worker_timing_details(connection, w->cb);
@@ -2130,13 +2128,13 @@ int drbd_worker(struct drbd_thread *thi)
                        update_worker_timing_details(connection, do_unqueued_work);
                        do_unqueued_work(connection);
                }
-               while (!list_empty(&work_list)) {
+               if (!list_empty(&work_list)) {
                        w = list_first_entry(&work_list, struct drbd_work, list);
                        list_del_init(&w->list);
                        update_worker_timing_details(connection, w->cb);
                        w->cb(w, 1);
-               }
-               dequeue_work_batch(&connection->sender_work, &work_list);
+               } else
+                       dequeue_work_batch(&connection->sender_work, &work_list);
        } while (!list_empty(&work_list) || test_bit(DEVICE_WORK_PENDING, &connection->flags));
 
        rcu_read_lock();