CSC/ECE 506 Spring 2011/ch2 JR

History

As computer architectures have evolved, so have parallel programming models. The earliest advancements in parallel computers took advantage of bit-level parallelism. These computers used vector processing, which required a shared memory programming model. As performance returns from this architecture diminished, the emphasis was placed on instruction-level parallelism and the message passing model began to dominate. Most recently, with the move to cluster-based machines, there has been an increased emphasis on thread-level parallelism. This has corresponded to an increase interest in the data parallel programming model.

Bit-level parallelism in the 1970's

The major performance improvements from computers during this time were due to the ability to execute 32-bit word size operations at one time (Culler (1999), p. 15.). The dominant supercomputers of the time, like the Cray and the ILLIAC IV, were mainly Single Instruction Multiple Data architectures and used a shared memory programming model. They each used different forms of vector processing (Culler (1999), p. 21.). Development of the ILLIAC IV began in 1964 and wasn't finished until 1975 [1]. A central processor was connected to the main memory and delegated tasks to individual PE's, which each had their own memory cache. [2]. Each PE could operate either an 8-, 32- or 64-bit operand at a given time [3].

The Cray machine was installed at Los Alamos National Laborartory in1976 by Control Data Corporation and had similar performance to the ILLIAC IV [4]. The Cray machine relied heavily on the use of registers instead of individual processors like the ILLIAC IV. Each processor was connected to main memory and had a number of 64-bit registers used to perform operations [CITE: http://www.eecg.toronto.edu/~moshovos/ACA05/read/cray1.pdf pg 65].

Move to instruction-level parallelism in the 1980's

Increasing the word size above 32-bits offered diminishing returns in terms of performance [CITE: Parallel Computer Architecture: A Hardware/Software Approach (The Morgan Kaufmann Series in Computer Architecture and Design) by David Culler, J.P. Singh, and Anoop Gupta (Hardcover – Aug 15, 1998) pg 15]. In the mid-1980's the emphasis changed from bit-level parallelism to instruction-level parallelism, which involved increasing the number of instructions that could be executed at one time [CITE: Parallel Computer Architecture: A Hardware/Software Approach (The Morgan Kaufmann Series in Computer Architecture and Design) by David Culler, J.P. Singh, and Anoop Gupta (Hardcover – Aug 15, 1998) pg 15]. The message passing model allowed programmers the ability to divide up instructions in order to take advantage of this architecture.

Thread-level parallelism

The move to cluster-based machines in the past decade, has added another layer of complexity to parallelism. Since computers could be located across a network from each other, there is more emphasis on software acting as a bridge [CITE: http://cobweb.ecn.purdue.edu/~pplinux/ppcluster.html]. This has led to a greater emphasis on thread- or task-level parallelism [CITE: http://en.wikipedia.org/wiki/Thread-level_parallelism] and the addition of the data parallelism programming model to existing message passing or shared memory models [CITE: http://en.wikipedia.org/wiki/Thread-level_parallelism].

References

• David E. Culler, Jaswinder Pal Singh, and Anoop Gupta, Parallel Computer Architecture: A Hardware/Software Approach, Morgan-Kauffman, 1999.
• Ian Foster, Designing and Building Parallel Programs, Addison-Wesley, 1995.
• Magne Haveraaen, "Machine and collection abstractions for user-implemented data-parallel programming," Scientific Programming, 8(4):231-246, 2000.
• W. Daniel Hillis and Guy L. Steele, Jr., "Data parallel algorithms," Communications of the ACM, 29(12):1170-1183, December 1986.
• Alexander C. Klaiber and Henry M. Levy, "A comparison of message passing and shared memory architectures for data parallel programs," in Proceedings of the 21st Annual International Symposium on Computer Architecture, April 1994, pp. 94-105.
• Yan Solihin, Fundamentals of Parallel Computer Architecture: Multichip and Multicore Systems, Solihin Books, 2008.