[PATCH v3 11/14] bfq: disable idle for prio_expire under better_fairness

[brookxu <brookxu.cn@gmail.com>]

From: Chunguang Xu <brookxu@tencent.com>

Under better_fairness, if higher priority queue is waiting
for service，disable queue idle, so that a schedule can be
invoked in time. In addition to CLASS_IDLE, other queues
allow idle, so that we can better control buffer IO too.

Signed-off-by: Chunguang Xu <brookxu@tencent.com>
---
 block/bfq-iosched.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index be5b1e3..5aa9c2c 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4307,6 +4307,14 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq)
 		return true;
 
 	/*
+	 * In better_fairness mode, we also put emphasis on Qos. The main
+	 * purpose of allowing idle here is to ensure better isolation
+	 * of Buffer IO.
+	 */
+	if (unlikely(bfqd->better_fairness))
+		return !(bfqd->bfq_slice_idle == 0 || bfq_class_idle(bfqq));
+
+	/*
 	 * Idling is performed only if slice_idle > 0. In addition, we
 	 * do not idle if
 	 * (a) bfqq is async
@@ -4318,6 +4326,9 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq)
 	   bfq_class_idle(bfqq))
 		return false;
 
+	if (bfq_may_expire_in_serv_for_prio(&bfqq->entity))
+		return false;
+
 	idling_boosts_thr_with_no_issue =
 		idling_boosts_thr_without_issues(bfqd, bfqq);
 
-- 
1.8.3.1