diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 98b15b98b85d7ed3837dc8fc1a663a71b2ee367a..69ecee7f4ad47b8b0f2a9c80bf66a7524130eef9 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3759,6 +3759,10 @@ static void *cfq_init_queue(struct request_queue *q)
 	cfqd->cfq_latency = 1;
 	cfqd->cfq_group_isolation = 0;
 	cfqd->hw_tag = -1;
+	/*
+	 * we optimistically start assuming sync ops weren't delayed in last
+	 * second, in order to have larger depth for async operations.
+	 */
 	cfqd->last_delayed_sync = jiffies - HZ;
 	INIT_RCU_HEAD(&cfqd->rcu);
 	return cfqd;