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>

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>
Shaohua Li · Jens Axboe
1 parent c1e44756fd
Showing 1 changed file with 22 additions and 1 deletions Side-by-side Diff
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);
+	}
 }
  
 /*
...	...	@@ -3255,6 +3255,10 @@
3255	3255	if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
3256	3256	return true;
3257	3257
	3258	+ /* An idle queue should not be idle now for some reason */
	3259	+ if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq))
	3260	+ return true;
	3261	+
3258	3262	if (!cfqd->active_cic \|\| !cfq_cfqq_wait_request(cfqq))
3259	3263	return false;
3260	3264
3261	3265
...	...	@@ -3508,8 +3512,25 @@
3508	3512	}
3509	3513	}
3510	3514
3511		- if (!cfqd->rq_in_driver)
	3515	+ if (!cfqd->rq_in_driver) {
3512	3516	cfq_schedule_dispatch(cfqd);
	3517	+ return;
	3518	+ }
	3519	+ /*
	3520	+ * A queue is idle at cfq_dispatch_requests(), but it gets noidle
	3521	+ * later. We schedule a dispatch if the queue has no requests,
	3522	+ * otherwise the disk is actually in idle till all requests
	3523	+ * are finished even cfq_arm_slice_timer doesn't make the queue idle
	3524	+ * */
	3525	+ cfqq = cfqd->active_queue;
	3526	+ if (!cfqq)
	3527	+ return;
	3528	+
	3529	+ if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq) &&
	3530	+ (!cfqd->cfq_group_idle \|\| cfqq->cfqg->nr_cfqq > 1)) {
	3531	+ cfq_del_timer(cfqd, cfqq);
	3532	+ cfq_schedule_dispatch(cfqd);
	3533	+ }
3513	3534	}
3514	3535
3515	3536	/*