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MPI & MPICH Presenter: Naznin Fauzia CSE 788.08 Winter 2012 - PowerPoint PPT Presentation

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MPI & MPICH Presenter: Naznin Fauzia CSE 788.08 Winter 2012 Outline MPI-1 standards MPICH-1 MPI-2 MPICH-2 MPI-3 Overview MPI (Message Passing Interface) Specification for a standard library for message passing

  1. MPI & MPICH Presenter: Naznin Fauzia CSE 788.08 Winter 2012

  2. Outline • MPI-1 standards • MPICH-1 • MPI-2 • MPICH-2 • MPI-3

  3. Overview • MPI (Message Passing Interface) • Specification for a standard library for message passing • Defined by MPI forum • Designed for high performance • on both massively parallel machines and on workstation clusters. • Widely available • both free available and vendor-supplied implementations

  4. Goals • To develop a widely used standard for writing message-passing programs. • Establish a practical, portable, efficient, and flexible standard for message passing. • Design an application programming interface (not necessarily for compilers or a system implementation library). • Allow efficient communication: Avoid memory-to-memory copying and allow overlap of computation and communication and offload to communication co-processor, where available. • Allow for implementations that can be used in a heterogeneous environment. • Allow convenient C and Fortran 77 bindings for the interface. • Assume a reliable communication interface: the user need not cope with communication failures. Such failures are dealt with by the underlying communication subsystem.

  5. Example #include <mpi.h> int main(int argc, char **argv){ /* Initialize MPI */ MPI_Init(&argc, &argv); /* Find out my identity in the default communicator */ int my_rank; MPI_Comm_rank(MPI_COMM_WORLD, &my_rank); int world_size; MPI_Comm_size(MPI_COMM_WORLD, &world_size); int number ; if (my_rank == 0) { number = -1; MPI_Send(&number, 1, MPI_INT, 1, 0, MPI_COMM_WORLD); } else if (my_rank == 1) { MPI_Recv(&number, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE); printf("Process 1 received number %d from process 0\n", number); } /* Shut down MPI */ MPI_Finalize(); return 0; }

  6. MPI-1 • Point-to-point communication • basic, pairwise communication (i.e., send and receive) • Collective operations • process-group collective communication operations (i.e., barrier, broadcast, scatter, gather, reduce ) • Process groups & communication contexts • how groups of processes are formed and manipulated, how unique communication contexts are obtained, and how the two are bound together into a communicator (i.e., MPI_COMM_WORLD) • Process topologies • explains a set of utility functions meant to assist in the mapping of process groups (a linearly ordered set) to richer topological structures such as multi- dimensional grids.

  7. MPI-1 contd. • Bindings for Fortran 77 and C • gives specific syntax in Fortran 77 and C, for all MPI functions, constants, and types. • Environmental Management and inquiry • explains how the programmer can manage and make inquiries of the current MPI environment • Profiling interface • ability to put performance profiling calls into MPI without the need for access to the MPI source code

  8. MPICH • Freely available implementation of MPI specification • Argonne National Laboratory, Mississippi State University • Portability and High-performance • “CH” => “Chameleon” • Symbol of adaptability • Other – LAM, CHIMP-MPI, Unify etc. • Focus on the work station environment

  9. Portability of MPICH • Distributed-memory Parallel Supercomputer • Intel Paragon, IBM SP2, Meiko CS-2, Thinking Machines CM-5, Ncube-2, Cray T3D • Shared-memory architectures • SGI Onyx, Challenge, Power Challenge, IBM SMP's the Convex Exempler, the Sequent Symmetry • Networks of Workstations • Ethernet-connected Unix workstations (may be of multiple vendors) • Sun, DEC, HP, SGI, IBM, Intel

  10. MPICH Architecture • ADI ( A bstract D evice I nterface ) • Central mechanism for portability • Many implementations of ADI • MPI functions are implemented in terms of ADI macros and function • Not MPI library specific – can be used for any high- level message passing library

  11. ADI • A set of function definitions • Four set of functions • Specifying a message to be sent or received • Moving data between the API and the message passing h/w • Managing list of pending messages (both sent or received) • Providing basic information about the execution environment (i.e., how many tasks are there)

  12. Upper Layer

  13. Lower Layer

  14. Features of MPICH • Groups • An ordered list of process identifiers • Stored as an integer array • Process's rank in a group is its index in the list • Communicators • MPICH intracommunicators and intercommunicators uses same structure • Both has a local group and a remote group – identical (intra) or disjoint (inter) • Send and receive context – equal (intra) or different (inter) • Contexts are integers

  15. Features of MPICH • Collective operations • Implemented on top of point-to-point operations • Some vendor-specific collective operations (Meiko, Intel and Convex) • Job Startup • MPI forum did not standardize the mechanism for starting jobs • mpirun mpirun -np 12 myprog

  16. Features of MPICH • Command-Line Arguments and Standard I/O mpirun –np 64 myprog –myarg 13 < data.in > results.out mpirun –np 64 –stdin data.in myprog –myarg 13 > results.out • Useful commands mpicc –c myprog.c

  17. MPE (Multi-Processing Environment) Extension Library • Parallel X graphics – routines to provide all processes with access to a shared X display • Logging – time stamped event trace file • Sequential sections – one process at a time, in rank order • Error handling – MPI_Errhandler_set

  18. Contributions of MPICH • MPICH has succeeded in popularizing the MPI standard • Encouraging vendors to provide MPI to their customers • By helping to create demand • By offering them a convenient starting point

  19. MPI-2 • Parallel I/O • Dynamic process management • One-sided communication • New language bindings – C++ & F90

  20. Sequential I/O 0 1 2 3 • Good for small process numbers (~100) and small datasets (~MB) • Not good for big process numbers (~ 100K) and big datasets (~TB)

  21. Parallel I/O FILE P(n-1) P0 P1 P2 • Multiple processes of a parallel program accessing data from a common file • Each process access a chunk of data using individual file pointers • MPI_File_open, MPI_File_seek, MPI_File_read, MPI_File_close

  22. One-Sided Communication • Remote Memory Access (RMA) • Window – specific region of process memory made available for RMA by other processes • MPI_Win_create – called by all processes within a communicator • Origin: the process that performs the call • Target: the process in which memory is accessed • Communication calls • MPI_Get: Remote read • MPI_Put: Remote write • MPI_accumulate

  23. One-sided communication MPI_Send MPI_Recv MPI_Get MPI_Put

  24. Dynamic process mgt. • MPI-1 • Does not specify how processes will be created • Does not allow processes to enter or leave a running parallel application • MPI-2 • Start new process, send them signals, find out when they die, establish communication between two processes

  25. MPICH-2 • ADI 3 – provides routines to support MPI-1 & 2 • Two types of RMA operations • Active target – target process must call an Mpi routine • Origin calls MPI_Win_start/MPI_Win_complete • Target calls MPI_Win_post/MPI_Win_wait • Passive target - target process not required to call any MPI routine • Origin calls MPI_Win_lock/MPI_Win_unlock

  26. MPICH-2 • Dynamic process • There are no absolute and global process ids • No data structure that map a process rank into a “global rank” (i.e., rank in MPI_COMM_WORLD) • All communications are considered locally in terms of possible virtual connections to processes • Arrays of virtual connections indexed by rank

  27. MPI-3 • Improved scalability • Better support for multi-core, cluster & application • Proposed => MPI_Count (larger than integer) • Extension of collective operations • Include non-blocking • Sparse collective operations • MPI_Sparse_gather

  28. MPI-3 • Extension of one-sided communication • To support RMA to arbitrary locations, no constraints (symmetric allocation or collective window creation) on memory • RMA operations that are imprecise (such access to overlapping storage) must be permitted, even if the behavior is undefined • The required level of consistency, atomicity, and completeness should be flexible • Read-modify-write operations and compare and swap are needed for efficient algorithms • MPI_Get_accumulate, MPI_Compare_and_swap • Backward compatibility

  29. References • http://www.mcs.anl.gov/research/projects/mpi/ • http://www.mpi-forum.org • A High-Performance, Portable Implementation of the MPI Message Passing Interface Standard - W. Gropp et al • MPI-2: Extending the Message Passing Interface - Al Geist et al • MPICH Abstract Device Interface, version 3.3 Reference Manual • http://meetings.mpi-forum.org/presentations/MPI_Forum_SC10.ppt.pdf • http://wissrech.ins.uni- bonn.de/teaching/seminare/technum/pdfs/iseringhausen_mpi2.pdf • www.sdsc.edu/us/training/workshops/docs

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