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SubjectRe: [RFC][PATCH] IO wait accounting
Rik van Riel <> writes:

> On Sun, 12 May 2002, Zlatko Calusic wrote:
>> Rik van Riel <> writes:
>> >
>> > And should we measure read() waits as well as page faults or
>> > just page faults ?
>> Definitely both.
> OK, I'll look at a way to implement these stats so that
> every IO wait counts as iowait time ... preferably in a
> way that doesn't touch the code in too many places ;)
>> Somewhere on the web was a nice document explaining
>> how Solaris measures iowait%, I read it few years ago and it was a
>> great stuff (quite nice explanation).
>> I'll try to find it, as it could be helpful.
> Please, it would be useful to get our info compatible with
> theirs so sysadmins can read their statistics the same on
> both systems.

Yes, that would be nice. Anyway, finding the document I mentioned will
be much harder than I thought. Googling last 15 minutes didn't make
progress. But, I'll keep trying.

Anyway, here is how Aix defines it:

Average percentage of CPU time that the CPUs were idle during which
the system had an outstanding disk I/O request. This value may be
inflated if the actual number of I/O requesting threads is less than
the number of idling processors.


Also, Sun has a nice collection of articles at, and among them which speaks
about wait time, but I'm still searching for a more technical document...
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