[PATCH BUGFIX IMPROVEMENT 12/14] block, bfq: port commit "cfq-iosched: improve hw_tag detection"

[Paolo Valente]

The original commit is
commit 1a1238a7dd48 ("cfq-iosched: improve hw_tag detection")
and has the following commit message.

If active queue hasn't enough requests and idle window opens, cfq will not
dispatch sufficient requests to hardware. In such situation, current code
will zero hw_tag. But this is because cfq doesn't dispatch enough requests
instead of hardware queue doesn't work. Don't zero hw_tag in such case.

Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
---
 block/bfq-iosched.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 48b579032d14..2ab53d93ba12 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4786,6 +4786,8 @@ static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
 
 static void bfq_update_hw_tag(struct bfq_data *bfqd)
 {
+	struct bfq_queue *bfqq = bfqd->in_service_queue;
+
 	bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
 				       bfqd->rq_in_driver);
 
@@ -4801,6 +4803,17 @@ static void bfq_update_hw_tag(struct bfq_data *bfqd)
 	if (bfqd->rq_in_driver + bfqd->queued <= BFQ_HW_QUEUE_THRESHOLD)
 		return;
 
+	/*
+	 * If active queue hasn't enough requests and can idle, bfq might not
+	 * dispatch sufficient requests to hardware. Don't zero hw_tag in this
+	 * case
+	 */
+	if (bfqq && bfq_bfqq_has_short_ttime(bfqq) &&
+	    bfqq->dispatched + bfqq->queued[0] + bfqq->queued[1] <
+	    BFQ_HW_QUEUE_THRESHOLD &&
+	    bfqd->rq_in_driver < BFQ_HW_QUEUE_THRESHOLD)
+		return;
+
 	if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
 		return;
 
-- 
2.20.1