TransCom: Transforming stream communication for load balance and efficiency in networks-on-chip

Recent work has examined using application-specific knowledge of streaming communication to optimize network routing (for throughput/performance) and/or design (for simpler hardware). Previous techniques have assumed that the communication streams are directly mapped to networks-on-chip. In contrast, this paper explores the use of communication transformations (TransCom) to achieve higher throughput via better network load balance and more efficient network utilization while retaining the communication semantics of the original streaming application. Specifically, we propose two transformations: stream fission and stream fusion. (While fission and fusion transformations have been applied to computation in streaming programs, we are the first to propose these transformations for stream communication.) Fission splits communication streams in to multiple streams that may be routed over independent network paths to achieve better network load balance. Fusion targets multicast communication and fuses multiple streams to effectively capture the well-known benefits of tree-based multicast, which include more efficient link utilization. Both techniques can be integrated in an integer linear program formulation that is solved at compile time. Evaluations with a suite of StreamIT benchmarks show that TransCom achieves significant performance improvement (nearly 60% on average) over prior application-specific (non-transformed) routing techniques.