Dynamic Scaling on MPI : MPI Process Provisioning / De-provisioning at Runtime

This is a header-only library to simplify the implementation of dynamic scaling on MPI 2.0. You can add or remove MPI processes during runtime. The added processes can communicate to the running processes immediately.

• Scale Out: Add new MPI processes to the running processes. The scaled processes join in the same MPI Intra-communicator as the running processes so that they can communicate each other.
• Scale In: Remove MPI processes from the running processes.

Reference

M. Hanai and G. Theodoropoulos "Performance Evaluation of Dynamic Scaling on MPI" (arXiv 2020)

Quick Start

$ git clone git@github.com:masatoshihanai/MPIDynamicScaling.git
$ cd MPIDynamicScaling
$ mkdir build; cd build
$ cmake ..; make
$ mpirun -np 2 ./DynamicScalingExample 2 1 

How to use

We provide the usage for (1) scaling out and (2) scaling in. See also the example code example/main_example.cpp.

1. Scale Out

There are two APIs for scaling out.

• scaleOut(MPI_Comm oldComm, int numAddProcs, string childCmd, MPI_Comm& newComm, vector<string> hosts) : This is used in the original program. The original program invokes new processes and waits for them to join the new intra-communicator.
  • oldComm is the original intra-communicator
  • newAddProcs is # additional MPI processes
  • childCmd is the path to Children's program.
  • newComm is the new intra-communicator including the additional processes. Their rank IDs are assigned incrementally.
  • hosts specifies additional hosts (optional). Each value is formatted as "host01" or "host01 slots=32" if you want to specify # slots.
• initNewProcess(MPI_Comm& newComm): This is used for the new processes invoked via scaleOut(). The new processes join to the new intra-communicator.
  • newComm: is the new intra-communicator.

2. Scale In

There is one API for scaling in.

• scaleIn(MPI_Comm& oldComm, bool isRemoving, MPI_Comm& newComm, bool& thisHostCanTerminate): The processes are removed after calling this function.
  • oldComm is the original communicator
  • isRemoving the process is removed if this value is true; otherwise the process keeps alive.
  • newComm is the new communicator excluding the removal processes.
  • thisHostCanTerminate is true if there are no MPI processes in this host (optional).

!!! Note !!! : The original MPI processes cannot be removed. Only ones added via scaleOut() can be removed.

How to integrate to your project

The library is hear-only. You may simply copy and include dynamic_scaling.hpp to your MPI code.

Tested Environment

• Open MPI 2.1.1 gcc/g++ 9.1.0

Contact

mhanai at acm.org