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Subject[PATCH] 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>
---
block/cfq-iosched.c | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index cfb0b2f..89b5dd9 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.
--
1.5.4.rc3


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