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Commit 6f816b4b authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

blk-mq: add optional request->alloc_time_ns 



There are currently two start time timestamps - start_time_ns and
io_start_time_ns.  The former marks the request allocation and and the
second issue-to-device time.  The planned io.weight controller needs
to measure the total time bios take to execute after it leaves rq_qos
including the time spent waiting for request to become available,
which can easily dominate on saturated devices.

This patch adds request->alloc_time_ns which records when the request
allocation attempt started.  As it isn't used for the usual stats,
make it optional behind CONFIG_BLK_RQ_ALLOC_TIME and
QUEUE_FLAG_RQ_ALLOC_TIME so that it can be compiled out when there are
no users and it's active only on queues which need it even when
compiled in.

v2: s/pre_start_time/alloc_time/ and add CONFIG_BLK_RQ_ALLOC_TIME
    gating as suggested by Jens.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent beab17fc

block/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -26,6 +26,9 @@ menuconfig BLOCK 


if BLOCK



config BLK_RQ_ALLOC_TIME

	bool



config BLK_SCSI_REQUEST

	bool

block/blk-mq.c

+11 −2
Original line number Diff line number Diff line
@@ -291,7 +291,7 @@ static inline bool blk_mq_need_time_stamp(struct request *rq) 
}



static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,

		unsigned int tag, unsigned int op)

		unsigned int tag, unsigned int op, u64 alloc_time_ns)

{

	struct blk_mq_tags *tags = blk_mq_tags_from_data(data);

	struct request *rq = tags->static_rqs[tag];
@@ -325,6 +325,9 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data, 
	RB_CLEAR_NODE(&rq->rb_node);

	rq->rq_disk = NULL;

	rq->part = NULL;

#ifdef CONFIG_BLK_RQ_ALLOC_TIME

	rq->alloc_time_ns = alloc_time_ns;

#endif

	if (blk_mq_need_time_stamp(rq))

		rq->start_time_ns = ktime_get_ns();

	else
@@ -356,8 +359,14 @@ static struct request *blk_mq_get_request(struct request_queue *q, 
	struct request *rq;

	unsigned int tag;

	bool clear_ctx_on_error = false;

	u64 alloc_time_ns = 0;



	blk_queue_enter_live(q);



	/* alloc_time includes depth and tag waits */

	if (blk_queue_rq_alloc_time(q))

		alloc_time_ns = ktime_get_ns();



	data->q = q;

	if (likely(!data->ctx)) {

		data->ctx = blk_mq_get_ctx(q);
@@ -393,7 +402,7 @@ static struct request *blk_mq_get_request(struct request_queue *q, 
		return NULL;

	}



	rq = blk_mq_rq_ctx_init(data, tag, data->cmd_flags);

	rq = blk_mq_rq_ctx_init(data, tag, data->cmd_flags, alloc_time_ns);

	if (!op_is_flush(data->cmd_flags)) {

		rq->elv.icq = NULL;

		if (e && e->type->ops.prepare_request) {

include/linux/blkdev.h

+12 −1
Original line number Diff line number Diff line
@@ -194,7 +194,11 @@ struct request { 


	struct gendisk *rq_disk;

	struct hd_struct *part;

	/* Time that I/O was submitted to the kernel. */

#ifdef CONFIG_BLK_RQ_ALLOC_TIME

	/* Time that the first bio started allocating this request. */

	u64 alloc_time_ns;

#endif

	/* Time that this request was allocated for this IO. */

	u64 start_time_ns;

	/* Time that I/O was submitted to the device. */

	u64 io_start_time_ns;
@@ -609,6 +613,7 @@ struct request_queue { 
#define QUEUE_FLAG_QUIESCED	24	/* queue has been quiesced */

#define QUEUE_FLAG_PCI_P2PDMA	25	/* device supports PCI p2p requests */

#define QUEUE_FLAG_ZONE_RESETALL 26	/* supports Zone Reset All */

#define QUEUE_FLAG_RQ_ALLOC_TIME 27	/* record rq->alloc_time_ns */



#define QUEUE_FLAG_MQ_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\

				 (1 << QUEUE_FLAG_SAME_COMP))
@@ -637,6 +642,12 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q); 
	test_bit(QUEUE_FLAG_SCSI_PASSTHROUGH, &(q)->queue_flags)

#define blk_queue_pci_p2pdma(q)	\

	test_bit(QUEUE_FLAG_PCI_P2PDMA, &(q)->queue_flags)

#ifdef CONFIG_BLK_RQ_ALLOC_TIME

#define blk_queue_rq_alloc_time(q)	\

	test_bit(QUEUE_FLAG_RQ_ALLOC_TIME, &(q)->queue_flags)

#else

#define blk_queue_rq_alloc_time(q)	false

#endif



#define blk_noretry_request(rq) \

	((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \