Massive manycore embedded processors with network-on-chip (NoC) architectures are becoming common. These architectures provide higher processing capability due to an abundance of cores. They provide native core-to-core communication that can be exploited via message passing to provide system scalability. Despite these advantages, manycores pose predictability challenges that can affect both performance and real-time capabilities. In this work, we develop efficient and predictable group communication using message passing specifically designed for large core counts in 2D mesh NoC architectures. We have implemented the most commonly used collectives in such a way that they incur low latency and high timing predictability making them suitable for balanced parallelization of scalable high-performance and embedded/real-time systems alike. Experimental results on a single-die 64 core hardware platform show that our collectives can significantly reduce communication times by up to 95 % for single packet messages and up to 98 % for longer messages with superior performance for sometimes all message sizes and sometimes only small message sizes depending on the group primitive. In addition, our communication primitives have significantly lower variance than prior approaches, thereby providing more balanced parallel execution progress and better real-time predictability.
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