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blk-mq: add optional request->alloc_time_ns

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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: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tejun Heo 2019-08-28 15:05:57 -07:00 committed by Jens Axboe
parent beab17fc2a
commit 6f816b4b74
3 changed files with 26 additions and 3 deletions
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3
block/Kconfig
View File

@ -26,6 +26,9 @@ menuconfig BLOCK
if BLOCK
config BLK_RQ_ALLOC_TIME
bool
config BLK_SCSI_REQUEST
bool

13
block/blk-mq.c
View File

@ -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) {

13
include/linux/blkdev.h
View File

@ -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| \