Commit 9d9b8895 authored Jun 09, 2019 by Konstantin Khlebnikov Committed by Jonathan Corbet Jun 14, 2019

block: document iostat changes for disk busy time accounting



Since commit 5b18b5a7 ("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>

parent 31753202

Documentation/iostats.txt

+4 −0

Original line number	Diff line number	Diff line
		@@ -97,6 +97,10 @@ Field 9 -- # of I/Os currently in progress
		Field 10 -- # of milliseconds spent doing I/Os
		This field increases so long as field 9 is nonzero.

		Since 5.0 this field counts jiffies when at least one request was
		started or completed. If request runs more than 2 jiffies then some
		I/O time will not be accounted unless there are other requests.

		Field 11 -- weighted # of milliseconds spent doing I/Os
		This field is incremented at each I/O start, I/O completion, I/O
		merge, or read of these stats by the number of I/Os in progress

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