[hobbit] CPU Utilization Not Correct or Averaging

[Henrik Stoerner]

On Fri, Dec 08, 2006 at 11:27:23AM -0600, James Wade wrote:

> I've had questions about CPU Utilization, The charts
> don't seem to correlate with the other two monitoring
> tools. As an example, The other tools show CPU
> Utilization at 80% during a couple hours at night,
> and Hobbit shows 26% Utilization. 

Make sure you understand what you're looking at. I assume you are
comparing the CPU utilisation from the vmstat data - the one on the
trends page, NOT the "CPU load" graph found on the "cpu" status page.
The "CPU load" graph shows the "5 minute load average", which has
nothing to do with CPU utilisation, but is a measure of how many tasks
are queuing up for the scheduler to allocate it some CPU time.

If you are looking at the vmstat graph, then by default you'll get
the plain "vmstat" graph which includes the time vmstat counts as
"system", "user" and "idle" time. Some systems also have an "I/O wait"
state; this is included in the "vmstat1" graph. Nightly jobs sound like
backups, these would show a high percentage of time in I/O wait state
which doesn't show up on the default vmstat graph. You can switch the
default graph by putting a "TRENDS:*,vmstat:vmstat1" on this host's
entry in the bb-hosts file.

> Both the other Tools show 80% utilization during those
> hours, but Hobbit doesn't.

Hobbit uses vmstat to collect these data from Unix systems - the command
"vmstat 2 300" specifically. I must admit I trust the built-in OS
commands to return valid data, more than I trust another monitoring tool 
whose method of determining these data I do not know.


Regards,
Henrik