A Multithreaded Multicore System for Embedded Media Processing

We describe a multicore system targeting media processing applications where the cores are multithreaded. The multithreaded cores use a new type of multithreading that we call Subset Static Interleaved (SSI) multithreading. SSI multithreading combines the advantages of blocked multithreading and a simple form of interleaved multithreading called static interleaved multithreading. SSI multithreading divides threads into foreground and background threads and performs static interleaving among the foreground threads. A foreground thread is swapped with a runnable background thread whenever the foreground thread is stalled. SSI multithreading achieves reduced operation latencies, memory latency tolerance, fast context switching, and compared to traditional dynamic interleaving, a relatively low design complexity of the register file.

We use a task scheduling unit (TSU) to dispatch tasks to the cores. The TSU is aware of the fact that the cores are multithreaded. This makes a more efficient mapping of tasks to cores possible by scheduling tasks on the least loaded cores.

We evaluate the system on an optimized Super HD H.264 decoder where the macroblock decoding and deblocking has been parallelized. The complexity of the H.264 standard and the high resolution makes this a challenging and performance demanding application. We achieve speedups of up to 17.7 times for 16 cores with four threads per core relative to a single-threaded single core. Furthermore, the proposed SSI multithreading achieves a speedup of 1.52 times relative to no multithreading, while blocked multithreading achieves only 1.38 times and a restricted form of interleaved multithreading achieves only 1.37 times speedup.