Date: Thu, 3 Dec 2009 11:51:35 +0800
From: Shaohua Li <shaohua.li@intel.com>
To: linux-kernel@vger.kernel.org
Cc: jens.axboe@oracle.com, akpm@linux-foundation.org
Subject: [PATCH]cfq-iosched: make nonrot check logic consistent
Message-ID: <20091203035135.GA13165@sli10-desk.sh.intel.com>
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Send again, last post seems lost.

cfq_arm_slice_timer() has logic to disable idle window for SSD device. The same
thing should be done at cfq_select_queue() too, otherwise we will still see
idle window. This makes the nonrot check logic consistent in cfq.
Tests in a intel SSD with low_latency knob close, below patch can triple disk
thoughput for muti-thread sequential read.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
 block/cfq-iosched.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux/block/cfq-iosched.c
===================================================================
--- linux.orig/block/cfq-iosched.c	2009-11-11 13:44:00.000000000 +0800
+++ linux/block/cfq-iosched.c	2009-11-11 13:45:33.000000000 +0800
@@ -1215,7 +1215,8 @@ static struct cfq_queue *cfq_select_queu
 	 * conditions to happen (or time out) before selecting a new queue.
 	 */
 	if (timer_pending(&cfqd->idle_slice_timer) ||
-	    (cfqq->dispatched && cfq_cfqq_idle_window(cfqq))) {
+	    (cfqq->dispatched && cfq_cfqq_idle_window(cfqq)
+	    && !(blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag))) {
 		cfqq = NULL;
 		goto keep_queue;
 	}
--
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