1 / 11

MPI Chapter 3

MPI Chapter 3. More Beginning MPI. MPI Philosopy. One program for all processes Starts with init Get my process number Process 0 is usually the “Master” node (One process to bind them all – apologies to J.R.R. Tolkien.) Big if/else statement to do master stuff verses slave stuff.

Download Presentation

MPI Chapter 3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. MPI Chapter 3 More Beginning MPI

  2. MPI Philosopy • One program for all processes • Starts with init • Get my process number • Process 0 is usually the “Master” node (One process to bind them all – apologies to J.R.R. Tolkien.) • Big if/else statement to do master stuff verses slave stuff. • Master could also do some slave stuff • Load balancing issues

  3. C++ MPI at WU on Herot • #include “mpi.h” • int main(int argc, char *argv[]) • MPI::Init(argc, argv) • Typically –np # to set up COMM_WORLD • mpic++ - to compile mpi programs • mpirun –np # • Plus stuff in Josh’s handout about system stuff

  4. Bcast • MPI::COMM_WORLD.Bcast(buf, count, datatype, root) • EVERY PROCESS executes this function. It is BOTH a send and receive. • Root is the “sender”, all other processes are receivers.

  5. Reduce • MPI::COMM_WORLD.Reduce(sendbuf, recvbuf, count, datatype, op, root) • Executed by ALL processes (somewhat of a send and receive). • EVERYONE sends sendbuf where op is performed on all those items and the answer appears in recvbuf of process root. • Op is specified by one of many constants (ex. MPI::SUM, MPI::PROD, MPI::MAX, MPI::MIN)

  6. Timing MPI Programs • double MPI::Wtime() • Time in seconds since some arbitrary point in time • Call twice, once at beginning, once at end of code to time • Difference is elapsed time • double MPI::Wtick() • Granularity, in seconds, of MPI Wtime function

  7. Receive revisited • Recall • MPI::COMM_WORLD.Recv(buf, count, datatype, source, tag, status) • Source and/or tag could be a wildcard (MPI::ANY_TAG, MPI::ANY_SOURCE) • Status type MPI::Status • int MPI::Status.Get_source() • int MPI::Status.Get_tag()

  8. Communicators • MPI_COMM_WORLD – has everything • Can create different communicators so can do operations with subgroups of processors

  9. Creating Communicators • MPI_Comm – data type for a communicator • MPI_Group – data type for a group • Can assign communicators (com1=com2) • Use a group of processors to create a communicator. • MPI_Comm_Group – gets the group from a communicator • MPI_Comm_create – create communicator from a group

  10. Communicator Manipulation • MPI_Group_excl – exclude a process from a group • MPI_Comm_free – releases communicator • MPI_Group_free

  11. Allreduce • Equivalent to reduce + Bcast.

More Related