commit 75ad23bc0fcb4f992a5d06982bf0857ab1738e9e
author Nick Piggin <npiggin@suse.de> Tue Apr 29 14:48:33 2008 +0200
committer Jens Axboe <jens.axboe@oracle.com> Tue Apr 29 14:48:33 2008 +0200
tree 8668ef63b1f420252ae41aed9e13737d49fd8054
parent 68154e90c9d1492d570671ae181d9a8f8530da55

block: make queue flags non-atomic

We can save some atomic ops in the IO path, if we clearly define
the rules of how to modify the queue flags.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/elevator.c

diff --git a/block/elevator.c b/block/elevator.c
index 88318c3..e8a90fe 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1070,7 +1070,7 @@
 	 */
 	spin_lock_irq(q->queue_lock);
 
-	set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+	queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
 
 	elv_drain_elevator(q);
 
@@ -1104,7 +1104,10 @@
 	 * finally exit old elevator and turn off BYPASS.
 	 */
 	elevator_exit(old_elevator);
-	clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+	spin_lock_irq(q->queue_lock);
+	queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+	spin_unlock_irq(q->queue_lock);
+
 	return 1;
 
 fail_register:
@@ -1115,7 +1118,11 @@
 	elevator_exit(e);
 	q->elevator = old_elevator;
 	elv_register_queue(q);
-	clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+
+	spin_lock_irq(q->queue_lock);
+	queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
+	spin_unlock_irq(q->queue_lock);
+
 	return 0;
 }