[netperf-talk] Help me to understand the results

[Rick Jones]

[discussions started in netperf-talk should remain there... ]

Steevan Rodrigues wrote:
> Hi Rick,
> 
> Thanks for the explanation. That really helped us.
> 
> I have one more question on CPU utilization reported by netperf.
> 
> Does netperf report CPU utilization for the "netperf" tool or is it 
> entire CPU utilization accounting for other tasks that are running ?
> 
> I am asking this question because I am seeing large difference between 
> CPU utilization reported by netperf and the "top" command.
> 
> Could you please clarify this?

Sadly, 
http://www.netperf.org/svn/netperf2/trunk/doc/netperf.html#CPU-Utilization does 
not address that directly.  I'll have to update it at some point.

Netperf believes it is measuring the CPU utilization of the entire system and 
ass-u-me-s it is the only source of that CPU utilization.   That said, with the 
advent of HW threading and such, measuring "CPU utilization" has become rather 
more complicated and depending on the system, and the method netperf is using 
(see the URL above) I could see where there might be discrepancies.

Based on the previous emails, and the netperf output contained therein, I would 
guess that the method being used by netperf is the /proc/stat method.  (The 'S' 
in the header portion for CPU utilization is the thing that makes me guess 
that).  There have been some "issues" in the past with format changes in 
/proc/stat that were not noticed by netperf.  You might compare the output of 
/proc/stat with the source code in src/netcpu_procstat.c  While doing-so, adding 
a -d to the global command line options to get the code to be a bit chatty about 
what it is doing might be goodness.

happy benchmarking,

rick jones