Optimizing the data cache performance of a software MPEG-2 video decoder

Abstract

Multimedia functionality has become an established component of core computer worHoads. MPEG-2 video decoding represents a particularly important and computationally demanding application example. Instruction set extensions like Intel’s MMX significantly reduce the computational challenges of this and other multimedia algorithms. However, memory subsystem deficiencies have now become the major barrier to increased performance, partly as a consequence of this improved CPU performance. Decoding MPEG-2 video data in software makes significant bandwidth demands on memory subsystems, which is seriously aggravated by cache ineficiencies. Conventional data caches generate many times more cache-memory trafic than required, at best double the minimum necessary to support decoding. Improving eficiency requires understanding the behavior of the decoder and composition of its data set. We provide an analysis of the memory and cache behavior of software MPEG-2 video decoding, and lay out a set of cache-oriented architectural enhancements which offer relief for the problem of excess cache-memory bandwidth. Our results show that cache-sensitive handling of different data types can reduce trafic by 50 percent or more.