[mrtg] Help - Clarification Sought

[Tony Hughes]

Guys

I would like to monitor cpu utilisation on a Nortel ARN.  There are two
ways I can do this as I see it.  First I can put a request to the MRTG
group for a sample config, which will solve my problem, but won't teach me
anything about how MRTG works.  So I am going to go with the harder way,
which is ask for clarification on a few points and concepts.

When I walk the mib tree using getif I find:-
 .wfResourceTotalEntry.wfResourceTotalCpuMax 
which has a definition of:-
 "The maximum amount of CPU time possible on this slot in centiseconds
since the slot started"

and

.wfResourceTotalEntry.wfResourceTotalCpuUsed
which has a definition of:-
"The amount of CPU used by all the entities on this slot in centiseconds
since the slot started"
There is also TotalCpuIdle OID too.

I created a cfg file using the CpuUsed OID and another that returns O thus:-
Target[mbah.cpu]:
1.3.6.1.4.1.18.3.3.2.5.7.1.2.1&1.3.6.1.4.1.18.3.1.4.2.1.5.1:public at 10.208.8.2
Title[mbah.cpu]: Murwillumbah System Stats
PageTop[mbah.cpu]:<H1>Murwillumbah CPU Utilisation</H1>
MaxBytes[mbah.cpu]: 100
Unscaled[mbah.cpu]: ymwd
Options[mbah.cpu]: growright,nopercent
LegendI[mbah.cpu]: &nbsp;cpu:
LegendO[mbah.cpu]: &nbsp;cpuo:
Ylegend[mbah.cpu]: percent
ShortLegend[mbah.cpu]: %
Legend1[mbah.cpu]: Total CPU Used
Legend2[mbah.cpu]: Total CPU Used


My question is how do I know that the value I am graphing is the actual
percentage of cpu utilisation?  Put differently, the log file is recording
the delta values for CpuUsed, and the graphs show these values increasing
and decreasing, but, is this value indicative of how much of the CPU is in
use?  I think that the % cpu utilisation should be something like
Percentage Used = CpuMax - CpuIdle*100/1.
If so then how do I do the maths?  I know this is a relatively simple
concept to understand, but the OID definitions are confusing to me as
CpuUsed is simply a number on its own unless referenced against CpuMax.

I apologise for the long posting, but I need to get my tiny brain around
this concept.
Thanks for any help guys.

Regards
Tony Hughes


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