Re: [Xenomai] Context Switch with rtnet

["Franz Engel" <franz_lambert_engel@yahoo.de>]

Hi Jan,

> > Hi,
> >
> > I've a little problem. I'm using the rtnet.h-header and the following
> function:
> > ret = recvfrom ( ethernetConnection.sock, &recBuffer, sizeof (
> > recBuffer ),0, ( struct sockaddr * )
> > &ethernetConnection.dest_addr,&destlen );
> >
> >
> > I compiled the program with the xenomai compiling flags and library.
> >
> > When I look to the xenomai state I get something like this:
> > CPU  PID    MSW        CSW        PF    STAT       %CPU  NAME
> >  22  0      0          834840     0     00000082    0.1  rtnet-stack
> >  22  0      0          1          0     00000082    0.0  rtnet-rtpc
> >   0  6262   2          2          0     00300380    0.0
> qs_robotpositio
> >   2  6265   2          6          0     00300380    0.0
> qs_robotpositio
> >   0  6266   1          1          0     00300380    0.0
> robotrsiinterfa
> >   1  6268   1147       2365       0     00300182    0.8
> robotrsiinterfa
> >
> > You can see, I get a lote of context and module switches just as the
> rtnet-stack itself. Is that normal?
> 
> Well, I have no clue what you configured, so I can only guess. If your
> task 6268 is a pure RT task that is not supposed to interact with Linux
> services, you first of all have a bug in your software stack. You
> should look for the reason of those mode switches to Linux, e.g. by
> asking Xenomai to raise SIGXCPU when this happens.

I use the SIGXCPU signal to look where I get a context switch. It is exactly
in the line of the recvfrom. I get the same result when I step through my
code. I debug from line to line and check the /proc/xenomai/state, so I can
see that the CSW and MSW increases when I step over the recvfrom. I tried my
code also with the native commands, like rt_recvfrom. But the result is the
same.

> 
> Regarding the rtnet-stack context switches: basically, every switch is
> one packet arriving at your NIC. Either you are receiving a lot of
> small but valid packets or you are on an open network, and that is
> basically heavy unrelated broadcast traffic of other sources than the
> RT device(s).
> 
> Jan

I'm connected to a robot that sends me his position every 4ms.

I send you a minimal example of my code. But I'm not sure if I understand
your question for the configuration correct. Depends the realtime capability
of rtnet only by my kdevelop project (cmake, *.c and *.h) or is it possible
that I miss some settings in the kernel? I start rtnet before I run my
program and I load the modules for my NIC and for UDP etc. Is there
something more what I have to do?

Thanks and regards,
    Franz

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