[CentOS] CPU usage over estimated?

Scott Silva ssilva at sgvwater.com
Thu Jun 4 21:54:10 UTC 2009


on 6-4-2009 2:14 PM Les Mikesell spake the following:
> Scott Silva wrote:
>> on 6-4-2009 5:37 AM Theo Band spake the following:
>>> I have a quad core CPU running Centos5.
>>>
>>> When I use top, I see that running processes use 245% instead of 100%.
>>> If I use gkrellm, I just see one core being used 100%.
>>>
>> This one is easy. 4 cpu's, 100% total each, a maximum of 400%.
>>
>> Since one core is at 100%, the other 145% is spread across the other 3 cores.
> 
> Is there any reasonable way to figure out the available CPU capacity 
> from an SNMP monitoring tool?  (You want to know if the reported >100% 
> usage is a problem but you don't know anything else about the machine).
> 
That can be difficult, because a machine in I/O wait can be slower than a
machine at full CPU utilization. There is nothing technically wrong with a
machine at 100% cpu. It is just means that the cpu is busy doing useful tasks,
instead of sitting idle doing nothing.
Where it is more critical is in a system that has occasional peaks of load. If
the system is already busy, then these tasks will wait. Unless your system
idles down and lowers the cpu freq. to save power, it isn't really saving
anything by being idle. As long as the system gets its work done in a timely
manner, then it isn't overloaded.

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