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January 1993


Alok Choudhary, Rajesh Bordawekar, Michael Harry, Divyesh Iadhav, Rakesh Krishnaiyer, Sachin More, K. Sivaram, Chutimet Srinilta, Rajeev Thakur, Syracuse University

I/O for parallel systems has drawn increasing attention in the last few years as it has become apparent that I/O performance, rather than CPU or communication performance, may be the limiting factor in future computing systems. Large-scale scientific computations, in addition to requiring a great deal of computational power, also deal with large quantities of data. At present, a typical Grand Challenge application could require 1 Gbyte to 4Tbytes of data per run. These figures are expected to increase by orders of magnitude as teraflop machines make their appearance.

Although supercomputers have very large main memories, the memory is not large enough to hold this much data. Hence, data needs to be stored on disk and the performance of the program depends on how fast the processors can access data from disks. Unfortunately, the performance of the I/O subsystems of MPPs has not kept pace with their processing and communications capabilities. A poor I/O capability can severely degrade the performance of the entire program. The need for high-performance I/O is so significant that almost all the present generation parallel computers provide some kind of hardware and software support for parallel I/O.

This group considers the I/O problem from a language, compiler, and runtime support point of view. The group is developing a compiler and runtime support system called PASSION: Parallel And Scalable Software for Input-Output. PASSION software support is targeted for I/O- intensive, out-of-core, loosely synchronous problems. The PASSION Runtime Library provides routines to efficiently perform the I/O required in out-of-core programs. The goal of the PASSION compiler is to translate out-of-core programs written in a data-parallel language like High Performance Fortran (HPF) to node programs with calls to the PASSION Runtime Library for I/O. Other components of the PASSION project include a Portable Parallel File System (VIP-FS), integrating task and data parallelism using parallel I/O and file servers for multimedia applications. The compiler, runtime system, and language work are being performed in collaboration with Rice University, University of Maryland, Argonne National Laboratory, and Caltech. This work is being performed as a part of the Scalable I/O initiative led by Caltech. (Go to the URL http://www.cacr.caltech.edu/SIO/ for information.)

A parallel processing environment with an I/O subsystem.

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