Data-type Dependent Cache Prefetching for MPEG Applications

Data cache prefetching is an effective technique to improve performance of cache memories, whenever the prefetching algorithm is able to correctly predict useful data to be prefetched. To this aim, adequate information on the program’s data locality must be used by the prefetching algorithm. In particular, multimedia applications are characterized by a substantial amount of image and video processing, which exhibits spatial locality in both the dimensions of the 2D data structures used for images and frames. However, in multimedia programs many memory references are made also to non-image data, characterized by standard spatial locality. In this work, we explore the adoption of different prefetching techniques in dependence of the data type (i.e., image and non-image), thus making itpossible to tune the prefetching algorithms to the differentforms of locality, and achieving overall performance optimization. In order to prevent interference between the two different data types, a split cache with two separated caches for image and non-image data is also evaluated as an alternative to a standard unified cache. Results on a multimedia workload (MPEG-2 and MPEG-4 decoders) show that standard prefetching techniques such as One-block-lookahead and the Stride Prediction Table are effective for standard data, while novel 2D prefetching techniques perform best on image data. In addition, at a parity of size, unified caches offer in general better performance that split caches, thank to the more flexible allocation of a unified cache space.