block: document iostat changes for disk busy time accounting
authorKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Sun, 9 Jun 2019 11:14:36 +0000 (14:14 +0300)
committerJonathan Corbet <corbet@lwn.net>
Fri, 14 Jun 2019 20:46:43 +0000 (14:46 -0600)
commit9d9b889540c380d8f56f7a79edbaae2fff8684d1
tree8763e2124944139c266c77a2c9c53869724e9547
parent31753202325dd4f9bba27fbbad05f189881c60bc
block: document iostat changes for disk busy time accounting

Since commit 5b18b5a73760 ("block: delete part_round_stats and switch to
less precise counting") io_ticks is approximated by adding one at each
start and end of requests if jiffies has changed.

This works perfectly for requests shorter than a jiffy. If requests runs
more than 2 jiffies some I/O time will not be accounted unless there are
other reuqests.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Documentation/iostats.txt