mpi.md

Faasm MPI support

Faasm provides a custom MPI implementation to execute existing unmodified MPI applications in a serverless context.

The Faasm MPI implementation is minimal but covers the majority of commonplace MPI functionality (point-to-point, collective, one-sided, custom datatypes).

MPI Functions

A number of MPI functions can be found at func/mpi. You can compile, upload and invoke hellompi with the following:

inv compile mpi hellompi
inv upload mpi hellompi
inv invoke mpi hellompi

Running code locally

To install the latest Open MPI locally you can use the following Ansible playbook:

cd ansible
ansible-playbook openmpi.yml --ask-become-pass

This installs it to /usr/local/faasm/openmpi.

Once you've built a native executable linked against this, you can then use mpirun on the binary e.g.

/usr/local/faasm/openmpi/bin/mpirun -n 2 <your native mpi func> 

ParRes Kernels

We can benchmark Faasm's MPI implementation using the ParRes Kernels modified slightly in the fork found in third-party/ParResKernels.

To compile and upload you can run the following:

inv libs.prk
inv upload.user prk

This uploads a number of the kernels written for MPI, e.g. nstream. These can be invoked using:

inv prk.invoke nstream

Extending the Faasm MPI implementation

The MPI interface declarations live in libs/faasmpi and the definitions in src/wasm/mpi.cpp.

Any new functions need to be included in libs/faasmpi/faasmpi.imports.