linux-kernel - [PATCH] blk-mq: determine in advance whether batch alloc can be performed

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Date:   Fri, 26 Aug 2022 09:26:30 +0800
From:   Liu Song <liusong@...ux.alibaba.com>
To:     axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] blk-mq: determine in advance whether batch alloc can be performed

From: Liu Song <liusong@...ux.alibaba.com>

Some conditions for judging whether batch alloc can be performed are
included in "blk_mq_get_tags", and this function is only used by
"__blk_mq_alloc_requests_batch".

This patch introduced a helper "can_do_batch_alloc" to prepend the
judgment condition and avoid unnecessary function calls.

Signed-off-by: Liu Song <liusong@...ux.alibaba.com>
---
 block/blk-mq-tag.c |  3 ---
 block/blk-mq.c     | 11 ++++++++++-
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 8e3b36d..cda3987 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -115,9 +115,6 @@ unsigned long blk_mq_get_tags(struct blk_mq_alloc_data *data, int nr_tags,
 	struct sbitmap_queue *bt = &tags->bitmap_tags;
 	unsigned long ret;
 
-	if (data->shallow_depth ||data->flags & BLK_MQ_REQ_RESERVED ||
-	    data->hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)
-		return 0;
 	ret = __sbitmap_queue_get_batch(bt, nr_tags, offset);
 	*offset += tags->nr_reserved_tags;
 	return ret;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3c1e6b6..330c618 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -437,6 +437,15 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
 	return rq_list_pop(data->cached_rq);
 }
 
+static inline bool can_do_batch_alloc(struct blk_mq_alloc_data *data)
+{
+	if (data->nr_tags > 1 && !(data->shallow_depth ||
+		data->flags & BLK_MQ_REQ_RESERVED ||
+		data->hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED))
+		return true;
+	return false;
+}
+
 static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
 {
 	struct request_queue *q = data->q;
@@ -480,7 +489,7 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
 	/*
 	 * Try batched alloc if we want more than 1 tag.
 	 */
-	if (data->nr_tags > 1) {
+	if (can_do_batch_alloc(data)) {
 		rq = __blk_mq_alloc_requests_batch(data, alloc_time_ns);
 		if (rq)
 			return rq;
-- 
1.8.3.1