cfq-iosched: improve sync vs async workloads

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

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index df82755ac40be58e4b4851ff9ef62edd79f05261..a8237be97a28d12e6684c7a6744ea9f881253a78 100644 (file)
--- 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;