linux-kernel - [PATCH 3/5] blk-mq: bitmap tag: select random tag betweet 0 and (depth

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Message-Id: <1399741312-10453-4-git-send-email-tom.leiming@gmail.com>
Date:	Sun, 11 May 2014 01:01:50 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Cc:	Ming Lei <tom.leiming@...il.com>
Subject: [PATCH 3/5] blk-mq: bitmap tag: select random tag betweet 0 and (depth - 1)

The selected tag should be selected at random between 0 and
(depth - 1) with probability 1/depth, instead between 0 and
(depth - 2) with probability 1/(depth - 1).

Signed-off-by: Ming Lei <tom.leiming@...il.com>
---
 block/blk-mq-tag.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 777aad7..77d2b18 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -427,7 +427,7 @@ void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *tag)
 {
 	unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
 
-	*tag = prandom_u32() % (depth - 1);
+	*tag = prandom_u32() % depth;
 }
 
 ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page)
-- 
1.7.9.5

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