[PATCH] cfq-iosched: fix slice_left calculation

[Tejun Heo <htejun@gmail.com>]

When cfq slice expires, remainder of slice is calculated and stored in
cfqq->slice_left.  Current code calculates the opposite of remainder -
how many jiffies the cfqq has used past slice end.  This patch fixes
the bug.

Signed-off-by: Tejun Heo <htejun@gmail.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -861,8 +861,8 @@ __cfq_slice_expired(struct cfq_data *cfq
 	 * store what was left of this slice, if the queue idled out
 	 * or was preempted
 	 */
-	if (time_after(now, cfqq->slice_end))
-		cfqq->slice_left = now - cfqq->slice_end;
+	if (time_after(cfqq->slice_end, now))
+		cfqq->slice_left = cfqq->slice_end - now;
 	else
 		cfqq->slice_left = 0;