Commits
Tejun Heo committed 6f816b4b746
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: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>