OSHMPI Notes

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Introduction
====================================

This project provides an OpenSHMEM 1.4 implementation on top of MPI-3.
MPI is the standard communication library for HPC parallel programming. OSHMPI
provides a lightweight OpenSHMEM implementation on top of the portable MPI-3
interface and thus can utilize various high-performance MPI libraries on
HPC systems.


====================================
Getting Started
====================================

1. Installation

    The simplest way to configure OSHMPI is using the following
    command-line:

        $ ./configure --prefix=/your/oshmpi/installation/dir CC=/path/to/mpicc

    Once you are done configuring, you can build the source and
    install it using:

        $ make
        $ make install

2. OSHMPI contains some simple test programs under the tests/ directory. For
   comprehensive test, we recommend using external test suites such as the
   SOS Test Suite (https://github.com/openshmem-org/tests-sos).

3. To compile an OpenSHMEM program with OSHMPI:
        $ /your/oshmpi/installation/dir/bin/oshcc -o test test.c
        or
        $ /your/oshmpi/installation/dir/bin/oshc++ -o test test.cpp

4. Use mpiexec to execute an OSHMPI program:
        $ /path/to/mpiexec -np 2 ./test

   For more information about the mpiexec command, please check the MPI
   library's documentation.


====================================
Support
====================================
If you have problems or need any assistance about the OSHMPI
installation and usage, please contact [email protected] mailing
list.


====================================
Bug Reporting
====================================
If you have found a bug in OSHMPI, please contact
[email protected] mailing list, or create an issue ticket on
github: https://github.com/pmodels/oshmpi.  If possible, please try to
reproduce the error with a smaller application or benchmark and send
that along in your bug report.


====================================
Configure Options
====================================
    --enable-fast (default no)
        Enable fast execution of OSHMPI implementation. It disables runtime
        control of debug message and disables all internal error checking.

    --enable-threads (default multiple)
        Choose OSHMPI thread safety level. For program uses single, funneled,
        or serialized thread levels, it is recommended to set the corresponding
        thread-safety in order to avoid internal overhead when possible. For
        instance, per-object critical section are enabled when multiple safety
        is set. Supported options include:
            single          - No threads (SHMEM_THREAD_SINGLE)
            funneled        - Only the main thread calls SHMEM (SHMEM_THREAD_FUNNELED)
            serialized      - User serializes calls to SHMEM (SHMEM_THREAD_SERIALIZED)
            multiple        - Fully multi-threaded (SHMEM_THREAD_MULTIPLE)

    --enable-amo (default auto)
        Choose AMO implementing methods.
        Because MPI-3 guarantees atomicity only for `same_op_no_op` or `same_op`
        accumulates, we cannot directly use MPI accumulates for OpenSHMEM atomic
        operations which can be `any_op`. Instead, we have to fallback all atomics
        to active message in OSHMPI. However, OSHMPI accepts special user hints
        which provide same restriction to same_op_no_op or same_op (see OSHMPI_AMO_OPS),
        hence direct AMO can be enabled at runtime. Supported options include:
           auto - runtime chooses direct or am methods based on user hints (default)
           direct - force to use direct atomics where all atomics uses MPI accumulates
           am - force to use active message based atomics.

    --enable-async-thread (default no)
        Enable asynchronous progress thread. Supported options include:
           yes - always enable asynchronous thread
           no - disable asynchronous thread (default)
           runtime - enable by setting environment variable OSHMPI_ENABLE_ASYNC_THREAD.

        Please note that the runtime option is useful for debugging use, however,
        it causes additional instruction at performance critical path.

====================================
Environment Variables
====================================
1. OpenSHMEM standard environment variables:

    SHMEM_SYMMETRIC_SIZE (default 128 MiB)
        Number of bytes to allocate for symmetric heap. The size value can be
        either number of bytes or scaled with a suffix of
            'K' or 'k' for kilobytes (B * 1024),
            'M' or 'm' for Megabytes (KiB * 1024)
            'G' or 'g' for Gigabytes (MiB * 1024)
            'T' or 't' for Terabytes (GiB * 1024)

    SHMEM_DEBUG (0|1, default 0)
        If defined enables debugging messages from OpenSHMEM runtime. It is
        invalid when configured with --enable-fast (see `--enable-fast`).

    SHMEM_VERSION (0|1, default 0)
        If defined prints SHMEM library version at start_pes(),
        shmem_init(), or shmem_init_thread().

    SHMEM_INFO (0|1, default 0)
        If defined prints SHMEM environment variables at stdout.

2. OSHMPI environment variables:

    OSHMPI_VERBOSE (0|1, default 0)
        If defined prints both SHMEM and OSHMPI environment variables at stdout.

    OSHMPI_AMO_OPS
        Defines the atomic operations used in the SHMEM program. If all PEs issue
        concurrent atomics only with the same operation, or with the same operation
        and fetch, then OSHMPI can directly utilize MPI accumulate operations.
        This is because, MPI grantees the atomicity of accumulate operations
        only with `same_op` or `same_op_no_op`. The default value of OSHMPI_AMO_OPS
        are  "cswap,finc,inc,fadd,add,fetch,set,swap,fand,and,for,or,fxor,xor".
        Arbitrary combination of the above operations can be given at execution
        time.

        The variable can be set only with configure `--enable-amo=auto` (see --enable-amo).

    OSHMPI_ENABLE_ASYNC_THREAD (0|1, default 0)
        Runtime control of asynchronous progress thread for atomic active message.
        When atomics cannot be directly translated to MPI accumulates (see OSHMPI_AMO_OPS),
        each atomic operations is issued via active-message based on the MPI two
        sided routines (i.e., MPI send/receive). If OSHMPI_ENABLE_ASYNC_THREAD
        is defined an internal thread is enabled to make asynchronous progress
        for the active message communication.

        The variable can be set only with configure `--enable-async-thread=runtime`
        (see --enable-async-thread) and `--enable-threads=multiple` (see --enable-thread).


====================================
Debugging Options
====================================
- Enable debugging flag by setting the configure option `--enable-g`.

- Set environment variable SHMEM_DEBUG=1 to print OSHMPI internal debugging message.


====================================
Test Framework
====================================
OSHMPI uses SOS Test Suite (https://github.com/openshmem-org/tests-sos) for
correctness test. The automatic test framework performs SOS tests on Ubuntu-64bit
platforms and uses MPICH-3.3rc1 and Open MPI 3.0 as the MPI provider. The test
status can be found at:
https://www.mcs.anl.gov/project/oshmpi/jenkins/

====================================
Known Issues
====================================
1. Some OpenSHMEM features are not supported in OSHMPI.
    a. Context
    OSHMPI cannot create separate or shared context on top of MPI interfaces.
    This feature may be enabled after the MPI end-point concept is accepted
    at MPI forum and implemented in MPI libraries. Current version always
    returns SHMEM_NO_CTX error at shmem_ctx_create(), and shmem_ctx_destroy()
    is a no-op.

2. OSHMPI does not provide Fortran APIs.

3. OSHMPI may not work on 32-bit platforms. This is because some internal routines
   rely on 64-bit integer, e.g., shmem_set_lock(), shmem_clear_lock(), shmem_test_lock.

4. OSHMPI may not correctly initialize symmetric data on OSX platform.