linux-kernel - [PATCH] CFQ: delay getting cfq group at the very point we really need it

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Date:	Thu, 15 Jul 2010 09:59:20 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>, Jens Axboe <axboe@...nel.dk>
CC:	Jeff Moyer <jmoyer@...hat.com>,
	Corrado Zoccolo <czoccolo@...il.com>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: [PATCH] CFQ: delay getting cfq group at the very point we really
 need it

Delay searching or allocating a cfq group at the very point that
we really need it. This change would save some cycles every time
we're getting a cfq queue.

Signed-off-by: Gui Jianfeng <guijianfeng@...fujitsu.com>
---
 block/cfq-iosched.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index eb4086f..9b0cf13 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2820,10 +2820,8 @@ cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync,
 {
 	struct cfq_queue *cfqq, *new_cfqq = NULL;
 	struct cfq_io_context *cic;
-	struct cfq_group *cfqg;
 
 retry:
-	cfqg = cfq_get_cfqg(cfqd, 1);
 	cic = cfq_cic_lookup(cfqd, ioc);
 	/* cic always exists here */
 	cfqq = cic_to_cfqq(cic, is_sync);
@@ -2852,6 +2850,9 @@ retry:
 		}
 
 		if (cfqq) {
+			struct cfq_group *cfqg;
+
+			cfqg = cfq_get_cfqg(cfqd, 1);
 			cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
 			cfq_init_prio_data(cfqq, ioc);
 			cfq_link_cfqq_cfqg(cfqq, cfqg);
-- 1.5.4.rc3 
--
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