This paper presents a study of the performance scalability of a macroblock-level parallelization of the H.264 decoder for High De nition (HD) applications on a multiprocessor architecture. We have implemented this parallelization on a cache coherent Non-uniform Memory Access (cc-NUMA) shared memory multiprocessor (SMP) and compared the results with the theoretical expectations. Three di erent scheduling techniques were analyzed: static, dynamic and dynamic with tail-submit. A dynamic scheduling approach with a tail-submit optimization presents the best performance obtaining a maximum speed-up of 9.5 using 24 processors. A detailed pro ling analysis showed that thread synchronization is one of the limiting factors for achieving a better parallel scalability. The paper includes an evaluation of the impact of using blocking synchronization APIs like POSIX threads and POSIX real-time extensions. Results showed that macroblock-level parallelism as a very negrain form of Thread-Level Parallelism (TLP) is highly affected by the thread synchronization overhead generated by these APIs. Other synchronization methods, possibly with hardware support, are required in order to make MB-level parallelization more scalable.

Peer Reviewed