Unlimited Vector Extension with Data Streaming Support

Abstract

Unlimited vector extension (UVE) is a novel instruction set architecture extension that takes streaming and SIMD processing together into the modern computing scenario. It aims to overcome the shortcomings of state-of-the-art scalable vector extensions by adding data streaming as a way to simultaneously reduce the overheads associated with loop control and memory access indexing, as well as with memory access latency. This is achieved through a new set of instructions that pre-configure the loop memory access patterns. These attain accurate and timely data prefetching on predictable access patterns, such as in multidimensional arrays or in indirect memory access patterns. Each of the configured data streams is associated to a general- purpose vector register, which is then used to interface with the streams. In particular, iterating over a given stream is simply achieved by reading/writing to the corresponding input/output stream, as the data is instantly consumed/produced. To evaluate the proposed UVE, a proof-of-concept gem5 implementation was integrated in an out-of-order processor model, based on the ARM Cortex-A76, thus taking into consideration the typical speculative and out-of-order execution paradigms found in high- performance computing processors. The evaluation was carried out with a set of representative kernels, by assessing the number of executed instructions, its impact on the memory bus and its overall performance. Compared to other state-of-the-art solutions, such as the upcoming ARM Scalable Vector Extension (SVE), the obtained results show that the proposed extension attains average performance speedups over 2.4 × for the same processor configuration, including vector length.