introduction to MPI

1. Using MPI
Kazuki Ohta

2. Using MPI

3. • HPC
• vendor/hardware
• program
•

4. MPI
• MPI: Message-Passing Interface
• API
• Communicator,Point-to-Point
Communication,Synchronization,One-Sided
Communication,Collective, Datatypes, MPI-I/O
•
• MPICH2 (ANL), MVAPICH (Ohio), OpenMP
• C/C++/Fortran support

5. •
• TCP/IP, Infiniband, Myrinet
• shared-memory
• OS
• MPICH2 Windows

6. • HW
• Infiniband, Myrinet NIC
• RDMA (Remote Direct Memory Access)

7. • Scales to 100,000 processes
• MPI on a Million Processors [Paven 2009]
• algorithm
• ” ”
• 1
•

8. • William D. Gropp
• http://www.cs.uiuc.edu/homes/wgropp/

9. • MPICH2
• Paven Balaj
• http://www.mcs.anl.gov/~balaji/
• Darius Buntinas
• http://www.mcs.anl.gov/~buntinas/

10. ( )
$ cd
$ echo “secretword=xxxx” > ~/.mpd.conf
$ cp .mpd.conf .mpdpasswd
$ chmod 600 .mpd.conf .mpdpasswd
$ echo “seduesearcher:16” > mpdhosts
$ mpdboot -n 1 -f mpdhosts
$ mpdtrace
seduesearcher

11. #include <mpi.h>
int main(int argc, char **argv)
{
int myrank;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
printf(“rank = %d¥n”, myrank);
MPI_Finalize();
}

12. $ mpicc hello.c
$ ruby -e ’16.times{ puts “seduesearcher” }’ >
machines
$ mpiexec -machinefile ./machines -n 16 ./a.out
rank = 4
rank = 2
rank = 0
rank = 1
rank = 8
rank = 3
.....

13. Point-to-Point
• 1 vs 1
• int MPI_Send(void *buf, int count,
MPI_Datatype datatype, int dest, int tag,
MPI_Comm comm);
• int MPI_Recv(void *buf, int count,
MPI_Datatype datatype, int source, int tag,
MPI_Comm, MPI_Status *status);
• Eager Protocol / Rendezvous Protocol

14. Point-to-Point
#include <mpi.h>
#include <string.h>
int
main(int argc, char **argv)
{
int nprocs;
int myrank;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
char msg[1024];
if (myrank == 0) {
strcpy(msg, "Hello, from rank0");
int dst;
for (dst = 1; dst < nprocs; dst++)
MPI_Send(msg, strlen(msg + 1), MPI_CHAR, dst, 99, MPI_COMM_WORLD);
} else {
MPI_Status status;
MPI_Recv(msg, 1024, MPI_CHAR, MPI_ANY_SOURCE, 99, MPI_COMM_WORLD, &status);
printf("rank%02d received: msg=%sn", myrank, msg);
}
MPI_Finalize();
}

15. • MPI
• /

16. MPI_Bcast

17. MPI_Scatter

18. MPI_Gather

19. MPI_AllGather
•

20. MPI_AlltoAll

21. MPI_Reduce

22. MPI_AllReduce

23. • MPI/IO
• I/O
• Two-Phase I/O
• Data Sieving

24. • BLAS
• GotoBLAS
• http://www.tacc.utexas.edu/tacc-projects/
• ScaLAPACK
• http://www.netlib.org/scalapack/
• ...

25. • MPI version 3
• MPI Forum
• http://meetings.mpi-forum.org/
• http://meetings.mpi-forum.org/
MPI_3.0_main_page.php
• Fault-Torelance
• Communication/Topology
• etc.