Re: [PATCH 5/15] cfq-iosched: speed up rbtree handling

[Alan D. Brunelle]

Hi Jens -

The attached patch speeds it up even more - I'm finding a >9% reduction 
in %system with no loss in IO performance. This just sets the cached 
element when the first is looked for.

Alan
From: Alan D. Brunelle <Alan.Brunelle@xxxxxx>

Update cached leftmost every time it is found.

Signed-off-by: Alan D. Brunelle <Alan.Brunelle@xxxxxx>
---

 block/cfq-iosched.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 8093733..a86a7c3 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -388,10 +388,10 @@ cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2)
  */
 static struct rb_node *cfq_rb_first(struct cfq_rb_root *root)
 {
-	if (root->left)
-		return root->left;
+	if (!root->left)
+		root->left = rb_first(&root->rb);
 
-	return rb_first(&root->rb);
+	return root->left;
 }
 
 static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)