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 6aa5523..b6491c0 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1057,6 +1057,14 @@
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 @@
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;
}