Re: [Xenomai] Context Switch with rtnet

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On 09/20/2012 05:24 PM, Franz Engel wrote:
> 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.

Stepping in gdb causes switches to secondary mode (each step is a switch
to secondary mode).

Anyway, you did not tell us:
- what version of xenomai
- what version of the Linux kernel
- what version of the I-pipe patch
- what architecture
- what NIC

you are using.

-- 
					    Gilles.