Chapter 8

Supporting cache-coherent collective communications


Across many architectures and parallel programming paradigms, collective communication plays a key role in performance and correctness. Hardware support is necessary to prevent important collective communication from becoming a system bottleneck. Support for multicast communication in networks-on-chip has achieved substantial throughput improvements and power savings. In this chapter, we explore support for reduction or many-to-one communication operations. As a case study, we focus on acknowledgement messages (ACK) that must be collected in a directory protocol before a cache line may be upgraded to or installed in the modified state. This chapter makes two primary contributions: ...

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