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>

1 files changed, 4 insertions, 6 deletions

diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 3ed2d871272e..d2d1f97511bd 100644
--- 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();