[netperf-talk] Re: CPU calibration

[Rick Jones]

Brijraj Vaghani wrote:
> Hi all,
> 
> I am trying to measure the CPU utilization of the IP/UDP stack on an
> embedded Linux environment. To measure the CPU utilization, I cross
> compiled Netperf for this particulate Linux environment and then
> executed it. The CPU utilization measurements returned U as Netperf
> was not aware of the Number of processors and CPU rate on the
> processor.

Ostensibly, "linux is linux" (well... :) and the /proc/stat stuff should 
work.  IIRC that would be --enable-cpuutil=procstat.

> Then as recommend in the manual ("some platforms have no particularly
> good mechanisms. On those platforms, it is probably best to use the
> "LOOPER" mechanism") I configured Netperf to use the LOOPER method to
> determine CPU utilization and executed it.
> The following is the result which I got for command line command
> netperf -H 10.195.16.226 -t UDP_STREAM -w 100 -b 8 -C -- -m 256

So, I see you then also did --enable-intervals right?

> Socket  Message  Elapsed     Messages                       CPU      
> Service
> Size      Size        Time         Okay Errors   Throughput   Util       
> Demand
> bytes    bytes       secs            #      #        10^6bits/sec % 
> UL     us/KB
> 
> 110592     256      30.63        4800      0        0.3     -1.00    -1.000
> 104448                30.63        4189                0.3     3.30     
> 965.666
> 
> The CPU utilization of 3.3% seems to be a little high of 0.3 Mbps of data.
> The manual also mentions that CPU calibration is needed when the
> LOOPER technique is used. As seen from my the command line, I did not
> specify the CPU rate. The debug trace on the machine running Netserver
> says "local maxrate = 316603 per sec". How do I validate this value of
> 316603??.

I suspect that while you asked for a 30 second run, the overall time was 
more like 70 seconds - that time was the netserver running the cpu util 
calibration code.  Actually, for the looper stuff it may even be a bit 
longer since it waits a bit for the looper process(es) to settle-in.

You could also run:

netperf -H <remote> -t REM_CPU

and it should give you its calibration value.  For a looper test all 
that really is is how quickly the looper process sits and spins in its 
little loop.  See src/netcpu_looper.c for details.

> The Linux environment on which I am running Netserver has 1 processor
> running at 624 MHz. Is there a way to calculate CPU rate of a
> particular processor, if yes then how? Also any other ideas on why the
> CPU utilization looks high?

Well, you could run top or vmstat - without netperf measuring CPU since 
the looper will take the system CPU util to 100% - and compare with what 
netperf reports for CPU util.

The 3.3% CPU util for 0.3 megabits per second could indeed be an 
artifact of the looper - there will be additional process/process 
context switching with the looper CPU util method.  Or it could just be 
high CPU utilization thanks to path length in the stack.

happy benchmarking,

rick jones

> 
> Looking forward to your response.
> 
> Thanks,
> Brijraj