PLX: An Instruction Set Architecture and Testbed for Multimedia Information Processing

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PLX is a concise instruction set architecture (ISA) that combines the most useful features from previous generations of multimedia instruction sets with newer ISA features for high-performance, low-cost multimedia information processing. Unlike previous multimedia instruction sets, PLX is not added onto a base processor ISA, but designed from the beginning as a standalone processor architecture optimized for media processing. Its design goals are high performance multimedia processing, general-purpose programmability to support an ever-growing range of applications, simplicity for constrained environments where low power and low cost are paramount, and scalability for higher performance in less constrained multimedia systems. Another design goal of PLX is to facilitate exploration and evaluation of novel techniques in instruction set architecture, microarchitecture, arithmetic, VLSI implementations, compiler optimizations, and parallel algorithm design for new computing paradigms.

Key characteristics of PLX are a fully subword-parallel architecture with novel features like wordsize scalability from 32-bit to 128-bit words, a new definition of predication, and an innovative set of subword permutation instructions. We demonstrate the use and high performance of PLX on some frequently-used code kernels selected from image, video, and graphics processing applications: discrete cosine transform, pixel padding, clip test, and median filter. Our results show that a 64-bit PLX processor achieves significant speedups over a basic 64-bit RISC processor and over IA-32 processors with MMX and SSE multimedia extensions. Using PLX’s wordsize scalability feature, PLX-128 often provides an additional 2× speedup over PLX-64 in a cost-effective way. Superscalar or VLIW (Very Long Instruction Word) PLX implementations can also add additional performance through inter-instruction, rather than intra-instruction parallelism. We also describe the PLX testbed and its software tools for architecture and related research.

Ruby B. Lee is the Forrest G. Hamrick Professor of Engineering and Professor of Electrical Engineering at Princeton University, with an affiliated appointment in the Computer Science department. She is the founder and director of the Princeton Architecture Laboratory for Multimedia and Security (PALMS). Her current research is in rethinking computer architecture for high-performance but low-cost security and multimedia processing. Prior to joining the Princeton faculty in 1998, Dr. Lee served as chief architect at Hewlett-Packard, responsible at different times for processor architecture, multimedia architecture, and security architecture for e-commerce and extended enterprises. She was a key architect in the initial definition and the evolution of the PA-RISC processor architecture used in HP servers and workstations. As chief architect for HP’s multimedia architecture team, Dr. Lee led an inter-disciplinary team focused on architecture to facilitate pervasive multimedia information processing using general-purpose computers. She introduced innovative multimedia instruction set architecture (MAX and MAX-2) in microprocessors, resulting in the industry’s first real-time, high-fidelity MPEG video and audio player implemented in software on low-end desktop computers. Dr. Lee also co-led an HP-Intel multimedia architecture team for IA-64, released in Intel’s Itanium microprocessors. Concurrent with full-time employment at HP, Dr. Lee also served as Consulting Professor of Electrical Engineering at Stanford University. Dr. Lee has a Ph.D. in Electrical Engineering and a M.S. in Computer Science, both from Stanford University, and an A.B. from Cornell University, where she was a College Scholar. She is a Fellow of ACM, a Fellow of IEEE, and a member of IS&T, Phi Beta Kappa, and Alpha Lambda Delta. She has been granted 115 U.S. and international patents, with several patent applications pending.
A. Murat Fiskiran is a Ph. D. student at the Department of Electrical Engineering at Princeton University. He is a member of the Princeton Architecture Laboratory for Multimedia and Security (PALMS) and a Kodak Fellow. His research interests include computer architecture and computer security.