linux-kernel - [PATCH v2 for-6.18/block 03/16] blk-mq: add QUEUE_FLAG_BIO_ISSUE

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Message-Id: <20250910063056.4159857-4-yukuai1@huaweicloud.com>
Date: Wed, 10 Sep 2025 14:30:43 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
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Subject: [PATCH v2 for-6.18/block 03/16] blk-mq: add QUEUE_FLAG_BIO_ISSUE_TIME

From: Yu Kuai <yukuai3@...wei.com>

bio->issue_time_ns is initialized for every bio, however, it's only used
by blk-iolatency. Add a new queue_flag and only set this flag when
blk-iolatency is enabled, so that extra blk_time_get_ns() can be saved
for disks that blk-iolatency is not enabled.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-iolatency.c  | 5 +++++
 block/blk-mq-debugfs.c | 1 +
 block/blk-mq.c         | 8 +++++---
 include/linux/blkdev.h | 1 +
 4 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index 554b191a6892..45bd18f68541 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -742,10 +742,15 @@ static void blkiolatency_enable_work_fn(struct work_struct *work)
 	 */
 	enabled = atomic_read(&blkiolat->enable_cnt);
 	if (enabled != blkiolat->enabled) {
+		struct request_queue *q = blkiolat->rqos.disk->queue;
 		unsigned int memflags;
 
 		memflags = blk_mq_freeze_queue(blkiolat->rqos.disk->queue);
 		blkiolat->enabled = enabled;
+		if (enabled)
+			blk_queue_flag_set(QUEUE_FLAG_BIO_ISSUE_TIME, q);
+		else
+			blk_queue_flag_clear(QUEUE_FLAG_BIO_ISSUE_TIME, q);
 		blk_mq_unfreeze_queue(blkiolat->rqos.disk->queue, memflags);
 	}
 }
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 32c65efdda46..4896525b1c05 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -96,6 +96,7 @@ static const char *const blk_queue_flag_name[] = {
 	QUEUE_FLAG_NAME(DISABLE_WBT_DEF),
 	QUEUE_FLAG_NAME(NO_ELV_SWITCH),
 	QUEUE_FLAG_NAME(QOS_ENABLED),
+	QUEUE_FLAG_NAME(BIO_ISSUE_TIME),
 };
 #undef QUEUE_FLAG_NAME
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2c0c8ead7080..31cc743ffad7 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -396,10 +396,12 @@ static inline void blk_mq_rq_time_init(struct request *rq, u64 alloc_time_ns)
 #endif
 }
 
-static inline void blk_mq_bio_issue_init(struct bio *bio)
+static inline void blk_mq_bio_issue_init(struct request_queue *q,
+					 struct bio *bio)
 {
 #ifdef CONFIG_BLK_CGROUP
-	bio->issue_time_ns = blk_time_get_ns();
+	if (test_bit(QUEUE_FLAG_BIO_ISSUE_TIME, &q->queue_flags))
+		bio->issue_time_ns = blk_time_get_ns();
 #endif
 }
 
@@ -3175,7 +3177,7 @@ void blk_mq_submit_bio(struct bio *bio)
 	if (!bio_integrity_prep(bio))
 		goto queue_exit;
 
-	blk_mq_bio_issue_init(bio);
+	blk_mq_bio_issue_init(q, bio);
 	if (blk_mq_attempt_bio_merge(q, bio, nr_segs))
 		goto queue_exit;
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c8cb08b2ed29..7c542b1851fa 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -657,6 +657,7 @@ enum {
 	QUEUE_FLAG_DISABLE_WBT_DEF,	/* for sched to disable/enable wbt */
 	QUEUE_FLAG_NO_ELV_SWITCH,	/* can't switch elevator any more */
 	QUEUE_FLAG_QOS_ENABLED,		/* qos is enabled */
+	QUEUE_FLAG_BIO_ISSUE_TIME,	/* record bio->issue_time_ns */
 	QUEUE_FLAG_MAX
 };
 
-- 
2.39.2