[PATCH 8/9] drbd: reduce lock contention in drbd_worker

From: Philipp Reisner
Date: Thu Sep 11 2014 - 08:32:17 EST


From: Lars Ellenberg <lars.ellenberg@xxxxxxxxxx>

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

Signed-off-by: Philipp Reisner <philipp.reisner@xxxxxxxxxx>
Signed-off-by: Lars Ellenberg <lars.ellenberg@xxxxxxxxxx>
---
drivers/block/drbd/drbd_worker.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 3ed2d87..d2d1f97 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();
--
1.9.1

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