1 files changed, 48 insertions, 6 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f41fdb5f3e0c..98b15b98b85d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2141,8 +2141,22 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
         /*
          * The active queue has run out of time, expire it and select new.
          */
-        if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq))
-                goto expire;
+        if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq)) {
+                /*
+                 * If slice had not expired at the completion of last request
+                 * we might not have turned on wait_busy flag. Don't expire
+                 * the queue yet. Allow the group to get backlogged.
+                 *
+                 * The very fact that we have used the slice, that means we
+                 * have been idling all along on this queue and it should be
+                 * ok to wait for this request to complete.
+                 */
+                if (cfqq->cfqg->nr_cfqq == 1 && cfqq->dispatched
+                    && cfq_should_idle(cfqd, cfqq))
+                        goto keep_queue;
+                else
+                        goto expire;
+        }
 
         /*
          * The active queue has requests and isn't expired, allow it to
@@ -3256,6 +3270,35 @@ static void cfq_update_hw_tag(struct cfq_data *cfqd)
                 cfqd->hw_tag = 0;
 }
 
+static bool cfq_should_wait_busy(struct cfq_data *cfqd, struct cfq_queue *cfqq)
+{
+        struct cfq_io_context *cic = cfqd->active_cic;
+
+        /* If there are other queues in the group, don't wait */
+        if (cfqq->cfqg->nr_cfqq > 1)
+                return false;
+
+        if (cfq_slice_used(cfqq))
+                return true;
+
+        /* if slice left is less than think time, wait busy */
+        if (cic && sample_valid(cic->ttime_samples)
+            && (cfqq->slice_end - jiffies < cic->ttime_mean))
+                return true;
+
+        /*
+         * If think times is less than a jiffy than ttime_mean=0 and above
+         * will not be true. It might happen that slice has not expired yet
+         * but will expire soon (4-5 ns) during select_queue(). To cover the
+         * case where think time is less than a jiffy, mark the queue wait
+         * busy if only 1 jiffy is left in the slice.
+         */
+        if (cfqq->slice_end - jiffies == 1)
+                return true;
+
+        return false;
+}
+
 static void cfq_completed_request(struct request_queue *q, struct request *rq)
 {
         struct cfq_queue *cfqq = RQ_CFQQ(rq);
@@ -3295,11 +3338,10 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
                 }
 
                 /*
-                 * If this queue consumed its slice and this is last queue
-                 * in the group, wait for next request before we expire
-                 * the queue
+                 * Should we wait for next request to come in before we expire
+                 * the queue.
                  */
-                if (cfq_slice_used(cfqq) && cfqq->cfqg->nr_cfqq == 1) {
+                if (cfq_should_wait_busy(cfqd, cfqq)) {
                         cfqq->slice_end = jiffies + cfqd->cfq_slice_idle;
                         cfq_mark_cfqq_wait_busy(cfqq);
                 }