cfq: Optimization for close cooperating queue searching

It doesn't make any sense to try to find out a close cooperating
queue if current cfqq is the only one in the group.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 5009af490a0c..b19cd684bf12 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1750,6 +1750,12 @@ static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
                 return NULL;
 
         /*
+         * Don't search priority tree if it's the only queue in the group.
+         */
+        if (cur_cfqq->cfqg->nr_cfqq == 1)
+                return NULL;
+
+        /*
          * We should notice if some of the queues are cooperating, eg
          * working closely on the same area of the disk. In that case,
          * we can group them together and don't waste time idling.