HPC across Heterogeneous Resources Sathish Vadhiyar

Motivation  MPI assumes global communicator with the help of which all processes can communicate with each other.  Hence all nodes on which MPI application is started must be accessible by all nodes.  This is not always possible  Due to the shortage of IP address space.  Security concerns – Large MPP sites and beowulf clusters have only 1 master node in public IP address space.  Grand challenging applications require the use of many MPPs.

PACX-MPI  Parallel Computer eXtension  MPI on a cluster of MPPs  Initially developed to connect Cray-YMP with Intel Paragon

PACX-MPI  CFDs or crash simulation of automobiles – 1 MPP not enough  Initial application – flow solver application across Pittsburgh supercomputing centre, Sandia national lab and High Performance Computing Center, Stuttgart  PACX sits between applications and MPI;

PACX-MPI  On each MPP, 2 extra nodes with running daemons to take care of communication between MPPs, compression and decompression of data, communication with local nodes  Daemon nodes implemented as additional local MPI processes  Communication among processes internal to MPP through vendor MPI on a local MPP network.  Communication between MPPs through daemons via Internet or specialized network.

PACX MPI Architecture

PACX MPI – Point-point comm. (Node 6 -> Node 2)

PACX MPI – Broadcast comm. (Root: Node 6)

Data Conversion  If the sender and receiver are in two separate heterogeneous MPPs, the sender converts its data to XDR (external data representation) format  Receiver converts data from XDR format to its own data representation

PACX-MPI: Results  Between T3Es at PSC and SDSC T3E  URANUS application  Navier-Strokes application – an iterative application based on convergence  Simulation of rentry vehicle  Between PSC and Univ. of Stuttgart  Closely coupled application due to frequent communication due to convergence.  Had to be modified for metacomputing setting – application made more asynchronous compromising on convergence  P3TDSMC – Monte Carlo for particle tracking  More amenable to metacomputing because of high computation- communication ratio  The latency effects are hidden as larger number of particles are considered.

Other Related Projects  PLUS  MPICH-G  PVMPI  MPI-Connect

References  Edgar Gabriel, Michael Resch, Thomas Beisel, Rainer Keller: 'Distributed computing in a heterogenous computing environment', (gzipped postscript) to appear at EuroPVMMPI'98 Liverpool/UK,  Thomas Beisel, Edgar Gabriel, Michael Resch: 'An Extension to MPI for Distributed Computing on MPPs' (gzipped postscript) in Marian Bubak, Jack Dongarra, Jerzy Wasniewski (Eds.) 'Recent Advances in Parallel Virtual Machine and Message Passing Interface', Lecture Notes in Computer Science, Springer, 1997,  Message-passing environments for metacomputing, Pages , Matthias A. Brune, Graham E. Fagg and Michael M. Resch, FGCS, Volume 15, 1999  PVMPI: An Integration of PVM and MPI systems.  A Grid-Enabled MPI: Message Passing in Heterogeneous Distributed Computing Systems. I. Foster, N. Karonis. Proc SC Conference, November, 1998