[mpich-discuss] MPI_Recv: MPI + Pthreads

Olya Krachina okrachin at purdue.edu
Wed Apr 23 10:10:21 CDT 2008

thank you for the slide links.... but my error was in not malloc-ing memory for 
resulting matrix...... the way to debug was to let each thread do nothing but 
one simple print, then i noticed that MPI_send buffer ptr was not valid....

Quoting Dmitri Chubarov <dmitri.chubarov at gmail.com>:

> Hello Olya, and all,
> >
> >  > Btw, the most common error people make while using threads (assuming
> all
> >  > threads perform MPI calls) is to use MPI_Init() -- you should use
> >  > MPI_Init_thread().
> >  I will try that..... i am not sure what you mean, but i am using threads
> on
> >  each MPI process, i.e. one MPI is an 8-pthread application.
> >
> multiple threads in an MPI process is what is often called "hybrid
> parallelization". There are two good sets of slides from Rolf
> Rabenseifner on the subject. The slides are some years old, and the
> experiments do not cover the MPICH2 implementation, and they are on
> using MPI + OpenMP, but since might be useful.
> Here is the first set of slides
> http://www.nsc.ru/cluster/A08_mpi_openmp_9.pdf
> It has some sort of taxonomy of programming models on page 8. I
> suppose your multiplication code leans to the right side where all
> threads communicate with each other with MPI through the boundaries of
> MPI processes.
> The second set of slides is this one:
> http://www.hlrs.de/organization/par/par_prog_ws/pdf/mpi_openmp_6.pdf
> Best regards,
>           Dima

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