cfq-iosched: improve continue or break logic in cfq_dispatch

This improves performance considerably for sync requests when you
have command queuing enabled.

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

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 6aa5523f514ccbf45bdd1d2bbeca3adf31299399..b6491c020f26ec53dedcbed84e20aea0a7aea299 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1057,6 +1057,14 @@ cfq_dispatch_requests(request_queue_t *q, int force)
                if (prev_cfqq == cfqq)
                        break;
 
+               /*
+                * 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 continued.
+                */
+               if (cfqd->rq_in_driver && cfq_cfqq_idle_window(cfqq))
+                       break;
+
                cfq_clear_cfqq_must_dispatch(cfqq);
                cfq_clear_cfqq_wait_request(cfqq);
                del_timer(&cfqd->idle_slice_timer);
@@ -1066,14 +1074,6 @@ cfq_dispatch_requests(request_queue_t *q, int force)
                        max_dispatch = 1;
 
                dispatched += __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
-
-               /*
-                * If the dispatch cfqq has idling enabled and is still
-                * the active queue, break out.
-                */
-               if (cfq_cfqq_idle_window(cfqq) && cfqd->active_queue)
-                       break;
-
                prev_cfqq = cfqq;
        }