Vector Microprocessors for Desktop Computing

Desktop workloads are expected to shift over the next few years to become increasingly media-centric. These multimedia applications require much larger computational demands than current desktop processors can provide. In this paper, we describe four major requirements that we believe any eeective desktop processor should address: it should meet the performance requirements of desktop workloads, it should exploit advances in VLSI fabrication technology to provide this performance, it should provide scalable performance for diierent processor generations with binary compatibility, and it should have mature compiler technology. We explain how vector microprocessors meet three of these requirements, but there is a perception that the performance for non-vectorizable codes would be unacceptably low. The rst half of this paper argues that current desktop workloads such as productivity applications and the SPEC95 integer benchmarks are either highly interactive or contain little exploitable parallelism. We explain how vector microprocessors should be able to exploit advances in VLSI technology to provide acceptable performance for these types of applications. There is also an important class of multimedia programs, such as MPEG2 decoding, that cannot be vectorized without extensive loop reorganization because their parallelism is in outer loops. In the second half of the paper, we quantitatively evaluate three compiler approaches that enable vectorization of outer loop parallelism: loop interchange, complete loop unrolling and outer-loop vectorization. We nd that, contrary to the standard practice of using loop interchange, outer-loop vectorization provides the greatest performance beneet of the three techniques for four multimedia benchmarks including the IDCT kernel from MPEG2 decoding.