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WASI MPI

WASI MPI is a WebAssembly embedder for MPI applications based on Wasmer. It supports WebAssembly modules that comply with the WebAssembly System Interface (WASI) specification. In addition to WASI, functions from the Message Passing Interface (MPI) specification can be used to enable distributed parallelization using WebAssembly.

Installation

Prebuilt Binaries

Every CI build of WASI MPI generates pre-built binaries for the following systems:

  • Ubuntu 16.04 or later + OpenMPI 4.1.1 (compile-linux)
  • OpenSUSE 15.1 + OpenMPI 4.0.4 (compile-linux-opensuse), this build is compatible with the execution environment on SuperMUC-NG
  • MacOS Big Sur + OpenMPI 4.1.1 (compile-macos)

They can be downloaded on the top right of the page as shown below:

pre_built_binaries.png

Compilation from Source

Prerequisites

  • Rust Compiler and Cargo
  • pkg-config (On Ubuntu, install pgk-config)
  • GCC with MPI compiler wrapper (On Ubuntu, install build-essential and openmpi-bin)
  • OpenSSL, zlib1g and OpenMPI development libraries (On Ubuntu, install libssl-dev, zlib1g-dev and libopenmpi-dev)
  • LLVM >= 11.0 (On Ubuntu, install llvm-11)

You can create a release build as follows:

cargo build --release

You might need to specify the location of the LLVM installation in the environment variable LLVM_SYS_110_PREFIX. You can identify the installation directory of LLVM by using which and ls:

ls -la $(which llvm-11-config)

The two binaries embedder and api will be placed in the ./target/release/ directory.

Usage

Embedder

Execute WebAssembly modules by supplying the path to them as the first argument to the embedder, any arguments following will be passed to the WebAssembly module verbatim:

./embedder my_module.wasm arg1 arg2

The embedder also supplies a help command:

embedder 0.1.0
Run WASI-MPI modules

USAGE:
    embedder [FLAGS] [OPTIONS] <MODULE_PATH> [--] [MODULE_ARGS]...

FLAGS:
    -h, --help       Prints help information
    -t, --timings
    -V, --version    Prints version information

OPTIONS:
    -c, --callback <callback>
    -d, --dir <dir>...

ARGS:
    <MODULE_PATH>
    <MODULE_ARGS>...

If you want to make use of the MPI functionality, you should run the embedder as an MPI job:

mpirun -np 8 ./embedder my_mpi_job.wasm

The embedder makes use of Wasmer's filesystem isolation. By default WebAssembly modules will not have access to the host's filesystem. (Any file I/O will fail with access denied.) If your WebAssembly module requires access to the host's filesystem you must explicitly grant it access to individual directories:

./embedder -d my_dir my_fs_module.wasm /my_dir

Paths given to the -d option are relative to your current working directory. Note that Wasmer employs path mapping for the WebAssembly module, for instance in the previous example the directory my_dir was given as a relative path but the argument to the WebAssembly module is an absolute path at the root of the filesystem. This is because any directory that you give access for is mapped at the root of the WebAssembly module's filesystem. You can give access to more than one directory:

./embedder -d dir1 -d dir2 -d dir3 my_fs_module.wasm /dir1 /dir2 /dir3

Compiling C/C++ applications for use with WASI MPI

Refer to the documentation in wasi-mpi-cpp-toolchain

The examples/ directory contains some prebuilt applications you may use to test your build of WASI MPI:

  • Intel MPI Benchmarks (imb.wasm)
  • HPCG Benchmark (xhpcg.wasm)
  • NPB IS Benchmark (npb-is-*-*.wasm)
  • NPB DT Benchmark (npb-dt-*-*.wasm)
  • IOR Benchmark (ior.wasm)