gstat shows > 100% busy
Poul-Henning Kamp
phk at phk.freebsd.dk
Sat Apr 16 12:46:54 PDT 2005
In message <42616975.9060303 at centtech.com>, Eric Anderson writes:
>Is gstat supposed to show > 100% sometimes? What does that mean,
>or is it a bug?
>
>dT: 0.501 flag_I 500000us sizeof 240 i -1
> L(q) ops/s r/s kBps ms/r w/s kBps ms/w %busy Name
> 2 260 146 14912 10.7 114 14565 2.8 148.1| ad0
> 0 0 0 0 0.0 0 0 0.0 0.0| ad0s1
The reason gstat shows >100% busy is that there are some outstanding
requests. (the 2 in the left hand column).
I tried to make the statistics collection as cheap as possible, and
as a side effect some of the columns can be somewhat misleading.
The length of the queue "L(q)" can be plain wrong due to a race in
updating the counters and %busy can go over 100% while there are
outstanding requests.
The sysctl kern.geom.collectstats can be used to tune some aspects
of the statistics collection, but the %busy issue is just something
you have to live with.
The reason why I don't want to spend cpu time on the %busy field
is that it is useless as a performance indication for all modern
disks and most ancient ones as well.
The "ms/r" and "ms/w" give you the time it takes to send a transaction
through (in milliseconds, for read and write respectively) and those
are the numbers you should monitor.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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