1 files changed, 24 insertions, 2 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index fb2141ec205..135b1a48da2 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -237,6 +237,7 @@ struct cfq_data {
         struct rb_root prio_trees[CFQ_PRIO_LISTS];
 
         unsigned int busy_queues;
+        unsigned int busy_sync_queues;
 
         int rq_in_driver;
         int rq_in_flight[2];
@@ -1344,6 +1345,8 @@ static void cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
         BUG_ON(cfq_cfqq_on_rr(cfqq));
         cfq_mark_cfqq_on_rr(cfqq);
         cfqd->busy_queues++;
+        if (cfq_cfqq_sync(cfqq))
+                cfqd->busy_sync_queues++;
 
         cfq_resort_rr_list(cfqd, cfqq);
 }
@@ -1370,6 +1373,8 @@ static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
         cfq_group_service_tree_del(cfqd, cfqq->cfqg);
         BUG_ON(!cfqd->busy_queues);
         cfqd->busy_queues--;
+        if (cfq_cfqq_sync(cfqq))
+                cfqd->busy_sync_queues--;
 }
 
 /*
@@ -2377,6 +2382,7 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
          * Does this cfqq already have too much IO in flight?
          */
         if (cfqq->dispatched >= max_dispatch) {
+                bool promote_sync = false;
                 /*
                  * idle queue must always only have a single IO in flight
                  */
@@ -2384,15 +2390,31 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
                         return false;
 
                 /*
+                 * If there is only one sync queue, and its think time is
+                 * small, we can ignore async queue here and give the sync
+                 * queue no dispatch limit. The reason is a sync queue can
+                 * preempt async queue, limiting the sync queue doesn't make
+                 * sense. This is useful for aiostress test.
+                 */
+                if (cfq_cfqq_sync(cfqq) && cfqd->busy_sync_queues == 1) {
+                        struct cfq_io_context *cic = RQ_CIC(cfqq->next_rq);
+
+                        if (sample_valid(cic->ttime_samples) &&
+                                cic->ttime_mean < cfqd->cfq_slice_idle)
+                                promote_sync = true;
+                }
+
+                /*
                  * We have other queues, don't allow more IO from this one
                  */
-                if (cfqd->busy_queues > 1 && cfq_slice_used_soon(cfqd, cfqq))
+                if (cfqd->busy_queues > 1 && cfq_slice_used_soon(cfqd, cfqq) &&
+                                !promote_sync)
                         return false;
 
                 /*
                  * Sole queue user, no limit
                  */
-                if (cfqd->busy_queues == 1)
+                if (cfqd->busy_queues == 1 || promote_sync)
                         max_dispatch = -1;
                 else
                         /*