[PATCH V5 09/12] blk-mq: limit hw queues to be polled in each blk_poll()

[Ming Lei <ming.lei@redhat.com>]

Limit at most 8 queues are polled in each blk_pull(), avoid to
add extra latency when queue depth is high.

Reviewed-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 79 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 55 insertions(+), 24 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 20bfc8c2d02e..e2701d502e51 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3865,36 +3865,31 @@ static inline int blk_mq_poll_hctx(struct request_queue *q,
 	return ret;
 }
 
-static int blk_mq_poll_io(struct bio *bio)
-{
-	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
-	blk_qc_t cookie = bio_get_private_data(bio);
-	int ret = 0;
+#define POLL_HCTX_MAX_CNT 8
 
-	/* wait until the bio is submitted really */
-	if (!blk_qc_t_ready(cookie))
-		return 0;
+static bool blk_add_unique_hctx(struct blk_mq_hw_ctx **data, int *cnt,
+		struct blk_mq_hw_ctx *hctx)
+{
+	int i;
 
-	if (!bio_flagged(bio, BIO_DONE) && blk_qc_t_valid(cookie)) {
-		struct blk_mq_hw_ctx *hctx =
-			q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
+	for (i = 0; i < *cnt; i++) {
+		if (data[i] == hctx)
+			goto exit;
+	}
 
-		ret += blk_mq_poll_hctx(q, hctx);
+	if (i < POLL_HCTX_MAX_CNT) {
+		data[i] = hctx;
+		(*cnt)++;
 	}
-	return ret;
+ exit:
+	return *cnt == POLL_HCTX_MAX_CNT;
 }
 
-static int blk_bio_poll_and_end_io(struct bio_grp_list *grps)
+static void blk_build_poll_queues(struct bio_grp_list *grps,
+		struct blk_mq_hw_ctx **data, int *cnt)
 {
-	int ret = 0;
 	int i;
 
-	/*
-	 * Poll hw queue first.
-	 *
-	 * TODO: limit max poll times and make sure to not poll same
-	 * hw queue one more time.
-	 */
 	for (i = 0; i < grps->nr_grps; i++) {
 		struct bio_grp_list_data *grp = &grps->head[i];
 		struct bio *bio;
@@ -3902,11 +3897,31 @@ static int blk_bio_poll_and_end_io(struct bio_grp_list *grps)
 		if (bio_grp_list_grp_empty(grp))
 			continue;
 
-		for (bio = grp->list.head; bio; bio = bio->bi_poll)
-			ret += blk_mq_poll_io(bio);
+		for (bio = grp->list.head; bio; bio = bio->bi_poll) {
+			blk_qc_t  cookie;
+			struct blk_mq_hw_ctx *hctx;
+			struct request_queue *q;
+
+			if (bio_flagged(bio, BIO_DONE))
+				continue;
+
+			/* wait until the bio is submitted really */
+			cookie = bio_get_private_data(bio);
+			if (!blk_qc_t_ready(cookie) || !blk_qc_t_valid(cookie))
+				continue;
+
+			q = bio->bi_bdev->bd_disk->queue;
+			hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
+			if (blk_add_unique_hctx(data, cnt, hctx))
+				return;
+		}
 	}
+}
+
+static void blk_bio_poll_reap_ios(struct bio_grp_list *grps)
+{
+	int i;
 
-	/* reap bios */
 	for (i = 0; i < grps->nr_grps; i++) {
 		struct bio_grp_list_data *grp = &grps->head[i];
 		struct bio *bio;
@@ -3931,6 +3946,22 @@ static int blk_bio_poll_and_end_io(struct bio_grp_list *grps)
 		}
 		__bio_grp_list_merge(&grp->list, &bl);
 	}
+}
+
+static int blk_bio_poll_and_end_io(struct bio_grp_list *grps)
+{
+	int ret = 0;
+	int i;
+	struct blk_mq_hw_ctx *hctx[POLL_HCTX_MAX_CNT];
+	int cnt = 0;
+
+	blk_build_poll_queues(grps, hctx, &cnt);
+
+	for (i = 0; i < cnt; i++)
+		ret += blk_mq_poll_hctx(hctx[i]->queue, hctx[i]);
+
+	blk_bio_poll_reap_ios(grps);
+
 	return ret;
 }
 
-- 
2.29.2