High CPU utilization at random times

[Scot Jenkins]

On 10/4/05, Dan Wilson <drw at adnc.com> wrote:
> I've been looking into a problem for quite some time now and have come
> up stumped.  Every time I think I know what the problem is I turn out to
> be wrong.
>
> Sorry, this is LONG but has lots of detail, hopefully all the detail you
> guys need to make a diagnosis or point me in the right direction :-)
>
> PROBLEM:
> Randomly, and for no good reason, the CPU usage on this machine will go
> up to anywhere from .7 to 1.5!?!?!?!?!?

A load average of 1.5 is not really all that high, especially if it's
not sustained for any lengthy period of time.  I've seen a heavily
loaded Linux mail server running with a load average of about 30, and
a FreeBSD system with a load average of over 100 (Apache went nuts
spawning CGI scripts).  Also keep in mind the load average is report
for the last 1, 5, and 15 minutes; man uptime(1) for details.  In
which field are you seeing the 1.5 load average?

Are you tracking disk IO some where?  sar and iostat (part of the
sysstat package) are good tools for this task.  You might want to
track and compare disk and CPU to see if they're related.  Since
you're running software RAID it could be that disk IO is causing the
CPU spike.

Check the Nagios "trends" CGI output and compare that with the output
from other tools:  vmstat, top (real-time), sar, iostat (real-time and
historical) to get a feel for what is normal for your system.

Scot


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