Re: [Discuss-gnuradio] How to balance workload among cores? Laptop cannot keep up with the USRP2 data flow.

[Jorge Miguel]

Hi !

Eric, thanks for your advise. Some results here.

I set my computer into "performance mode". At first sight nothing improves.

With the example usrp2_fft.py I can low the decimation to 5 and the application works ok.


As I said the FM modulator works ok by itself. The FM demodulator also works ok by itself. The problem is when I run both in the same flowgraph. I think it is not a problem of performance since my CPUs are not very work-loaded when my application is running.

My problem is that changes, in the FM modulator, which I think they would increase performance (like increasing my 13 interpolation in the USRP and decreasing my software interpolation) make my receiver chain non-working (SSS messages) although the transmitter outputs a perfect FM signal.

I do not understand these mesages since my CPUs are less than 15-20% used. However something is stopping the received data because I got a lot of dropped frames in my rx Ethernet interface (saw with ifconfig). I tried to increase the RX Ethernet buffer (sysctl -w net.core.rmem_max=XXXXX) but it didn't work. I also tried to set in my generated code the USRP source instance before the USRP sink but it didn't work neither.

Could be any reason why by decreasing software computation (and Ethernet traffic as well) in the transmitter path affects the performance of the RX path?

Many thanks,
Jorge.

On 28 September 2010 05:43, Eric Blossom <address@hidden> wrote:

On Mon, Sep 27, 2010 at 10:07:07AM +0200, Jorge Miguel wrote:
> Hi all!
>
> I am Tx/Rx a FM signal at the same time, but I can see a lot of SSSSS
> messages that mean my CPU cannot keep up with all frames generated by the
> USRP2 and drop most of them.
> However I have a quite new laptop with a CPU:Intel(R) Core(TM) i5 CPU
> M 520  @ 2.40GHz  on Ubuntu 10.4
>
> I guess that my laptop is enough to run my FM Tx/Rx and I wonder if I can
> balance the workload among all my four cores to see if my application
> improves (ethernet interface doens't drop any frame).
>

First off, you don't really have 4 cores.  You've got 2 cores +
hyperthreading (they may have renamed it, but that's what you've got).

GNU Radio will automatically use whatever you've got, without you
having to do anything special.

Be sure that your laptop is in "Performance mode", and not trying to
save energy, or throttle back etc.  There are also some laptops out
there that have poor thermal design and can't really run at full speed
without overheating and thus throttling back the CPU.

Start with something like usrp_fft.py and see how low of a decimation
factor you can work with reliably.  That will give you a basic idea of
how your system is working.

If you're building your own flow graphs, it's quite easy to string
together more blocks, or use a a higher sample rate, than your machine
can keep up with.

After you've ruled out the stuff above, oprofile will help you sort
out which parts of your application are burning the most time.

Eric