[netperf-talk] Re: CPU calibration

[Brijraj Vaghani]

Thanks a lot Rick. I think the numbers make a lot of sense after using
procstat instead of LOOPER on an embedded linux setup.

I was also curious to know if the data transfer in Netperf between
user and kernel space is mmapapped or through data copies? This
information would help me determine in which portion of the processor
is spending most of its time.

Thanks,
Brijraj

On 7/9/07, Rick Jones <rick.jones2 at hp.com> wrote:
> > I reconfigured Netperf with --enable-cpuutil=procstat and executed the
> > same test. The results look slightly different but still a little off.
> > To process 0.3 Mpbs of data it takes 2.9% CPU. The additional 0.4% in
> > case of LOOPER might be because of the artifacts.
>
> Agreed - the use of LOOPER is not without overhead.
>
>  > Using TOP I observed
> > the CPU utilization of the Netserver process. It oscillates between
> > 0.1% to 0.3%. Any ideas as to why this discrepancy?
>
> Well, not all the CPU consumed on behalf of netperf will be charged to
> the netperf process.  That probably isn't all the difference though it
> might close the gap if you look at top's report of overall CPU util.
>
> I suppose there is a possibility of math errors with such low CPU utils
> - there is IIRC some integer math happening there.  You might increase
> the traffic rate by one or two orders of magnitude and revisit the
> comparison.
>
> netperf uses the stats exported via /proc/stat - I suppose that some
> manual calculations could also be done as a sanity check of netperf's math.
>
> rick jones
>
>