cfq-iosched: improve sync vs async workloads

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 18 insertions, 13 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index df82755ac40b..a8237be97a28 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -96,6 +96,7 @@ struct cfq_data {
         struct hlist_head *cfq_hash;
 
         int rq_in_driver;
+        int sync_flight;
         int hw_tag;
 
         /*
@@ -911,11 +912,15 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
  */
 static void cfq_dispatch_insert(request_queue_t *q, struct request *rq)
 {
+        struct cfq_data *cfqd = q->elevator->elevator_data;
         struct cfq_queue *cfqq = RQ_CFQQ(rq);
 
         cfq_remove_request(rq);
         cfqq->dispatched++;
         elv_dispatch_sort(q, rq);
+
+        if (cfq_cfqq_sync(cfqq))
+                cfqd->sync_flight++;
 }
 
 /*
@@ -1100,27 +1105,24 @@ static int cfq_dispatch_requests(request_queue_t *q, int force)
         while ((cfqq = cfq_select_queue(cfqd)) != NULL) {
                 int max_dispatch;
 
-                if (cfqd->busy_queues > 1) {
-                        /*
-                         * So we have dispatched before in this round, if the
-                         * next queue has idling enabled (must be sync), don't
-                         * allow it service until the previous have completed.
-                         */
-                        if (cfqd->rq_in_driver && cfq_cfqq_idle_window(cfqq) &&
-                            dispatched)
+                max_dispatch = cfqd->cfq_quantum;
+                if (cfq_class_idle(cfqq))
+                        max_dispatch = 1;
+
+                if (cfqq->dispatched >= max_dispatch) {
+                        if (cfqd->busy_queues > 1)
                                 break;
-                        if (cfqq->dispatched >= cfqd->cfq_quantum)
+                        if (cfqq->dispatched >= 4 * max_dispatch)
                                 break;
                 }
 
+                if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq))
+                        break;
+
                 cfq_clear_cfqq_must_dispatch(cfqq);
                 cfq_clear_cfqq_wait_request(cfqq);
                 del_timer(&cfqd->idle_slice_timer);
 
-                max_dispatch = cfqd->cfq_quantum;
-                if (cfq_class_idle(cfqq))
-                        max_dispatch = 1;
-
                 dispatched += __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
         }
 
@@ -1767,6 +1769,9 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
         cfqd->rq_in_driver--;
         cfqq->dispatched--;
 
+        if (cfq_cfqq_sync(cfqq))
+                cfqd->sync_flight--;
+
         if (!cfq_class_idle(cfqq))
                 cfqd->last_end_request = now;