block: elevator quiescing helpers

Simple helper functions to quiesce the request queue. These are
currently only used for switching IO schedulers on-the-fly, but
we can use them to properly switch IO accounting on and off as well.

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

2 files changed, 31 insertions, 13 deletions

diff --git a/block/blk.h b/block/blk.h
index 3ee94358b43d..22043c2886c7 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -70,6 +70,10 @@ void blk_queue_congestion_threshold(struct request_queue *q);
 
 int blk_dev_init(void);
 
+void elv_quisce_start(struct request_queue *q);
+void elv_quisce_end(struct request_queue *q);
+
+
 /*
  * Return the threshold (number of used requests) at which the queue is
  * considered to be congested.  It include a little hysteresis to keep the
diff --git a/block/elevator.c b/block/elevator.c
index ca6788a0195a..c6744913ff4a 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -587,6 +587,31 @@ static void elv_drain_elevator(struct request_queue *q)
         }
 }
 
+/*
+ * Call with queue lock held, interrupts disabled
+ */
+void elv_quisce_start(struct request_queue *q)
+{
+        queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
+
+        /*
+         * make sure we don't have any requests in flight
+         */
+        elv_drain_elevator(q);
+        while (q->rq.elvpriv) {
+                blk_start_queueing(q);
+                spin_unlock_irq(q->queue_lock);
+                msleep(10);
+                spin_lock_irq(q->queue_lock);
+                elv_drain_elevator(q);
+        }
+}
+
+void elv_quisce_end(struct request_queue *q)
+{
+        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+}
+
 void elv_insert(struct request_queue *q, struct request *rq, int where)
 {
         struct list_head *pos;
@@ -1101,18 +1126,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
          * Turn on BYPASS and drain all requests w/ elevator private data
          */
         spin_lock_irq(q->queue_lock);
-
-        queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
-
-        elv_drain_elevator(q);
-
-        while (q->rq.elvpriv) {
-                blk_start_queueing(q);
-                spin_unlock_irq(q->queue_lock);
-                msleep(10);
-                spin_lock_irq(q->queue_lock);
-                elv_drain_elevator(q);
-        }
+        elv_quisce_start(q);
 
         /*
          * Remember old elevator.
@@ -1136,7 +1150,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
          */
         elevator_exit(old_elevator);
         spin_lock_irq(q->queue_lock);
-        queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+        elv_quisce_end(q);
         spin_unlock_irq(q->queue_lock);
 
         blk_add_trace_msg(q, "elv switch: %s", e->elevator_type->elevator_name);