Improved SIMD architecture for high performance video processors

摘要

Single instruction multiple data (SIMD) execution is in no doubt an efficient way to exploit the data level parallelism in image and video applications. However, SIMD execution bottlenecks must be tackled in order to achieve high execution efficiency. We first analyze in this paper the implementation of two major kernel functions of H.264/AVC namely, SATD and subpel interpolation, in conventional SIMD architectures to identify the bottlenecks in traditional approaches. Based on the analysis results, we propose a new SIMD architecture with two novel features: 1) parallel memory structure with variable block size and word length support, and 2) configurable SIMD structure. The proposed parallel memory structure allows great flexibility for programmers to perform data access of different block sizes and different word lengths. The configurable SIMD structure allows almost random register file access and slightly different operations in ALUs inside SIMD. The new features greatly benefit the realization of H.264/AVC kernel functions. For instance, the fractional motion estimation, particularly the half to quarter pixel interpolation, can now be executed with minimal or no additional memory access. When comparing with the conventional SIMD systems, the proposed SIMD architecture can have a further speedup of 2.1X to 4.6X when implementing H.264/AVC kernel functions. Based on Amdahl's law, the overall speedup of H.264/AVC encoding application can be projected to be 2.46X. We expect significant improvement can also be achieved when applying the proposed architecture to other image and video processing applications.