[netperf-talk] Some question about CPU utilization

[Rick Jones]

Benjamin Thery wrote:
> Hi,
> 
> I'm using netperf to do some network benchmarking on Linux and
> I have some questions regarding CPU utilization.
> 
> Very often, um... most of the time, when I run netperf I get the
> "!!! WARNING, Desired confidence was not achieved within the specified
> iterations.". It's _always_ due to variations in CPU util.

How far away from your desired interval (10%) is netperf reporting?

> What can I do to stabilize the CPU util on my host?
> Are there some known tricks?

One is to bind netperf and netserver to a specific CPU with the global 
-T option.

> Should I increase the number of iterations or the duration of the test?
> 
> Here are some additional informations:
> 
> I run netperf with the following options : -I 95,10 -i 10,2
> and I set the test duration to 40 seconds.

I'd suggest going with -i 30,3 .  30 is the maximum netperf will do, and 
3 is the minimum - your setting was getting silently set to 3 for the 
minimum :)

> 
> CPU util is measured between 1 and 2% (very low CPU load).
> 
> My test machine is a bi-processor dual-core Xeon 5130 2GHz.

What sort of test is this with that low a CPU load?  IIRC the linux 
procstat CPU util method is "statistical" and at such a low load level I 
get a little "concerned" about the measurments.  If going to 30 
iterations doesn't give you stability, you may also want to try 
increasing the iteration runtime to 120 seconds.

> I tried to run CPU_LOC test.
> It returns immediatly and givethe value 100.
> (I thought I read in the manual this test should last 40 sec?)

You may have - although depending on which manual you are reading, it 
may also discuss now how some CPU util methods don't require 
calibration, so the *_CPU tests will return "immediately."  The linux 
procstat method is such a method.

happy benchmarking,

rick jones