check_load --- divide by number of cpus?

Hugo van der Kooij hvdkooij at vanderkooij.org
Sat May 10 09:31:29 CEST 2008


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Terry wrote:
| I am sitting here racking my brain on this one.  Is dividing the load
| average by the number of CPUs a smart thing to do?  the 'uptime'
| command on a box does not do this.  So, if I have an 8 core box
| sitting with a load average of 8, its the same as a single core box
| sitting with a load average of 1?  I'll see the same type of server
| response?  Thoughts?

The load value is the least understood value of a unix system. Most
people simple do not know how to handle it.

I have created situations with a load of just 1 and a CPU usage of 100%
where a second session becomes sluggish. And I have also created
situation where the same system had a load of around 12 and I could
happely hack away on the system at the same time.

By itself the load factor is not very usefull. Take into account the CPU
usage and I/O actions and you start to get a proper picture.

If you are to do any maths on the load factor you should not divide it
by the number of CPU's. Doing a substraction would give a slightly less
distorted figure if you start to mangle with the numbers.

Say you use the following value for a single core CPU:
define service{
~        use                             local-service         ; Name of
service template to use
~        host_name                       balin.waakhond.net
~        service_description             Current Load
~        check_command
check_local_load!5.0,4.0,3.0!10.0,6.0,4.0
~        }

Then basically I would add 7 to all these counters for a 8 core system.

Hugo.


- --
hvdkooij at vanderkooij.org               http://hugo.vanderkooij.org/
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