linux-kernel - [PATCH] cfq-iosched: avoid slice overrun when idling

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Date:	Wed, 7 Oct 2009 10:59:00 +0200
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	"Linux-Kernel" <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Jeff Moyer <jmoyer@...hat.com>
Subject: [PATCH] cfq-iosched: avoid slice overrun when idling

Idle window for a queue is reduced when the queue is about to finish
its slice.

Signed-off-by: Corrado Zoccolo <czoccolo@...il.com>
---
 block/cfq-iosched.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 4ab33d8..55bb8ca 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1105,8 +1105,10 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
 	 * we don't want to idle for seeks, but we do want to allow
 	 * fair distribution of slice time for a process doing back-to-back
 	 * seeks. so allow a little bit of time for him to submit a new rq
+	 * but avoid overrunning its timeslice
 	 */
-	sl = cfqd->cfq_slice_idle;
+	sl = min_t(unsigned long, cfqd->cfq_slice_idle,
+		cfqq->slice_end - jiffies);
 	if (sample_valid(cic->seek_samples) && CIC_SEEKY(cic))
 		sl = min(sl, msecs_to_jiffies(CFQ_MIN_TT));
 
-- 
1.6.2.5



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