From: nap [mailto:napar...@gmail.com]
Sent: Tuesday, April 02, 2013 2:48 AM
To: Nagios Users List
Subject: Re: [Nagios-users] Help with CPU Check Thresholds
On Mon, Apr 1, 2013 at 2:05 PM, Scott Wilkerson
<swilker...@nagios.com<mailto:swilker...@nagios.com>> wrote:
Alex,
It would be very common for a machine with multiple CPU's to have a
higher load. On a 16 CPU machine, no processes would be waiting at all
with a load under 16.
Hi,
Yes if all the load is consumed by CPUs, but it's quite rare. For example with
a database the most time is spend on disks I/O, and a 16cpu server won't help
here, you can be overload with a load average > 1 in this case.
The "good" load average is very specific for each server/application. CPU
number is a just a part of the "load" equation.
Jean
I think that's rather a misunderstanding of what load average is. It is not
based on the CPU (otherwise it would be called something stupid like CPU % on
Windows). There's lots of resources on the Googles that explain what goes into
the load average calculation so I won't go into it here, but it is intended to
be a general number indicating the load of the system and i/o wait times are
definitely a factor in that calculation. It is intended to be a
representation of how busy a machine is overall. The general rule is as Scott
indicates that for a machine with 'n' CPUs (cores, kind of as well) if the load
average is also 'n' then that machine is 100% utilized. That is, it is
completely able to keep up with what it's being asked to do. If the load
average is '2n' then it's 200% utilized and the machine is effectively getting
behind.
But anyway, there are some really good write-ups as to how the load average
calculation is made, but it's definitely not just CPU. CPU utilization by
itself is pretty useless nowadays in my opinion.
Mark
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