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->pre_start_time_ns which records when the
request allocation attempt started. As it isn't used for the usual
stats, make it optional behind QUEUE_FLAG_REC_PRESTART.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
block/blk-mq.c | 11 +++++++++--
include/linux/blkdev.h | 7 ++++++-
2 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index e5ef40c603ca..90b46988cc02 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -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 pre_start_time_ns)
{
struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
struct request *rq = tags->static_rqs[tag];
@@ -325,6 +325,7 @@ 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;
+ rq->pre_start_time_ns = pre_start_time_ns;
if (blk_mq_need_time_stamp(rq))
rq->start_time_ns = ktime_get_ns();
else
@@ -356,8 +357,14 @@ static struct request *blk_mq_get_request(struct request_queue *q,
struct request *rq;
unsigned int tag;
bool clear_ctx_on_error = false;
+ u64 pre_start_time_ns = 0;
blk_queue_enter_live(q);
+
+ /* pre_start_time includes depth and tag waits */
+ if (blk_queue_rec_prestart(q))
+ pre_start_time_ns = ktime_get_ns();
+
data->q = q;
if (likely(!data->ctx)) {
data->ctx = blk_mq_get_ctx(q);
@@ -393,7 +400,7 @@ 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, pre_start_time_ns);
if (!op_is_flush(data->cmd_flags)) {
rq->elv.icq = NULL;
if (e && e->type->ops.prepare_request) {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 259bd7ad8312..4247a9bc44b7 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -194,7 +194,9 @@ struct request {
struct gendisk *rq_disk;
struct hd_struct *part;
- /* Time that I/O was submitted to the kernel. */
+ /* Time that the first bio started allocating this request. */
+ u64 pre_start_time_ns;
+ /* 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;
@@ -606,6 +608,7 @@ struct request_queue {
#define QUEUE_FLAG_SCSI_PASSTHROUGH 23 /* queue supports SCSI commands */
#define QUEUE_FLAG_QUIESCED 24 /* queue has been quiesced */
#define QUEUE_FLAG_PCI_P2PDMA 25 /* device supports PCI p2p requests */
+#define QUEUE_FLAG_REC_PRESTART 26 /* record pre_start_time_ns */
#define QUEUE_FLAG_MQ_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_SAME_COMP))
@@ -632,6 +635,8 @@ 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)
+#define blk_queue_rec_prestart(q) \
+ test_bit(QUEUE_FLAG_REC_PRESTART, &(q)->queue_flags)
#define blk_noretry_request(rq) \
((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \
--
2.17.1
