cfq-iosched: schedule dispatch for noidle queue
A queue is idle at cfq_dispatch_requests(), but it gets noidle later. Unless
other task explictly does unplug or all requests are drained, we will not
deliever requests to the disk even cfq_arm_slice_timer doesn't make the
queue idle. For example, cfq_should_idle() returns true because of
service_tree->count == 1, and then other queues are added. Note, I didn't
see obvious performance impacts so far with the patch, but just thought
this could be a problem.
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index b8174bb..986865e 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3255,6 +3255,10 @@
if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
return true;
+ /* An idle queue should not be idle now for some reason */
+ if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq))
+ return true;
+
if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
return false;
@@ -3508,8 +3512,25 @@
}
}
- if (!cfqd->rq_in_driver)
+ if (!cfqd->rq_in_driver) {
cfq_schedule_dispatch(cfqd);
+ return;
+ }
+ /*
+ * A queue is idle at cfq_dispatch_requests(), but it gets noidle
+ * later. We schedule a dispatch if the queue has no requests,
+ * otherwise the disk is actually in idle till all requests
+ * are finished even cfq_arm_slice_timer doesn't make the queue idle
+ * */
+ cfqq = cfqd->active_queue;
+ if (!cfqq)
+ return;
+
+ if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq) &&
+ (!cfqd->cfq_group_idle || cfqq->cfqg->nr_cfqq > 1)) {
+ cfq_del_timer(cfqd, cfqq);
+ cfq_schedule_dispatch(cfqd);
+ }
}
/*