[PATCH] cfq-iosched: improve queue preemption

Don't touch the current queues, just make sure that the wanted queue
is selected next. Simplifies the logic.

Signed-off-by: Jens Axboe <axboe@suse.de>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9f684cc66bd1631042d7d53fe9c5e52f6cbb3e54..1411048359524fdc5f86a89c47733f1a1dac9f42 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1539,17 +1539,19 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
  */
 static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 {
-       struct cfq_queue *__cfqq, *next;
-
-       list_for_each_entry_safe(__cfqq, next, &cfqd->cur_rr, cfq_list)
-               cfq_resort_rr_list(__cfqq, 1);
+       cfq_slice_expired(cfqd, 1);
 
        if (!cfqq->slice_left)
                cfqq->slice_left = cfq_prio_to_slice(cfqd, cfqq) / 2;
 
+       /*
+        * Put the new queue at the front of the of the current list,
+        * so we know that it will be selected next.
+        */
+       BUG_ON(!cfq_cfqq_on_rr(cfqq));
+       list_move(&cfqq->cfq_list, &cfqd->cur_rr);
+
        cfqq->slice_end = cfqq->slice_left + jiffies;
-       cfq_slice_expired(cfqd, 1);
-       __cfq_set_active_queue(cfqd, cfqq);
 }
 
 /*