From 9d9b889540c380d8f56f7a79edbaae2fff8684d1 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Sun, 9 Jun 2019 14:14:36 +0300 Subject: [PATCH] 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 Signed-off-by: Jonathan Corbet --- Documentation/iostats.txt | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/Documentation/iostats.txt b/Documentation/iostats.txt index 49df45f90e8a..5d63b18bd6d1 100644 --- a/Documentation/iostats.txt +++ b/Documentation/iostats.txt @@ -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