Performance Impact of Unaligned Memory Operations in SIMD Extensions for Video Codec Applications

—Although SIMD extensions are a cost effective way to exploit the data level parallelism present in most media applications, we will show that they had have a very limited memory architecture with a weak support for unaligned memory accesses. In video codec, and other applications, the overhead for accessing unaligned positions without an efficient architecture support has a big performance penalty and in some cases makes vectorization counter-productive. In this paper we analyze the performance impact of extending the Altivec SIMD ISA with unaligned memory operations. Results show that for several kernels in the H.264/AVC media codec, unaligned access support provides a speedup up to 3.8X compared to the plain SIMD version,

• Type: Conference
• Year: 2007
• Where: ISPASS
• Authors: Mauricio Alvarez, Esther Salamí, Alex Ramírez, Mateo Valero
• Keywords: Altivec SIMD ISA, ISPASS 2007, SIMD, SIMD Extensions, Software Engineering