Re: [Xenomai-help] Xenomai and OpenMP

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

Eric Noulard wrote:
> 2009/3/6 Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>:
>> M. Koehrer wrote:
>>> Hi everybody,
>>>
>>> is it possible to use OpenMP with Xenomai Realtime threads? I have a
>>> Intel QuadCore CPU running. Currently I use the native skin to create
>>> multiple threads to run on multiple CPU cores. That works perfectly.
>>> However for some computations, a more local parallel computation
>>> could be great. And OpenMP provides exactly the right thing here. My
>>> question is now: Is it possible to use OpenMP with Xenomai real time
>>> tasks? How can I define the worker threads of OpenMP to be real time
>>> threads? What about the priority of these threads?
>> I do not know what OpenMP is,
> 
> OpenMP is a proposed standard for shared-memory parallel programming:
> http://openmp.org.
> 
> The idea is to indicate to the OpenMP-aware compiler which part
> of your code may be parallelized with #pragma omp <something>
> those pragma should be ignored by non OpenMP-aware compiler
> making the parallelized code more portable.
> 
> GCC 4.2 and up support OpenMP pragma if you use the
> -fopenmp
> command line switch.
> 
>> but if it uses the posix API, the first
>> step to make it work with Xenomai is to try and compile it with xenomai
>> posix skin. Then, all threads created by this openmp compiled for
>> xenomai posix skin will be real-time threads, and the priority of these
>> threads will be the one chosen by the pthread_att_setschedparam or
>> pthread_setschedparam services.
> 
> The OpenMP parallel model concerning threads is a so-called
> fork/join model. The compiler insert the code that
> creates the threads (and eventually join them)
> at appropriate places for you.
> The work is then distributed to those "worker" threads.
> The code use to handle those mechanism is NOT under user control,
> user only insert OpenMP pragmas.
> 
> In GCC there is a supporting library "libgomp" used:
> http://gcc.gnu.org/viewcvs/trunk/libgomp/
> 
> the lib seems to be using pthread, but this as to be checked carefully.
> Thus I would bet that somewhere in libgomp you'll find the pthread_xxxx
> calls corresponding to the OpenMP handled threads.
> 
> I think in order to make the OpenMP thread Xenomai one's you'll have
> to find WHERE (in the libgomp code) they are created and may
> WHEN they are launched, in order to be sure the libgomp created
> threand will be Xenomai tasks.
> 
> The solution used by other compiler to support OpenMP may be different,
> so the Xenomai+OpenMP support may be different  for other compiler.

if the libgomp uses posix, recompiling it for xenomai posix skin should
be enough.

-- 
                                                 Gilles.