Design and Evaluation of Traffic Filter for Token Protocol

Cache coherence protocols play an important role in maintaining data coherence in shared-memory multiprocessor. Token protocol provides a flexible framework for designing new coherence protocols. It features in both attributes: low-latency cache misses and no reliance on totally-ordered inter-connects. However, messages in token protocol are always broadcasted, which limits the scalability of token-based protocol. In this paper, a traffic filter is proposed to reduce the net-work traffic of token protocol. It records the information of the recently used blocks. When a miss happens, the requested block is checked in the traffic filter, and broadcasting can be avoided if existing. With traffic filter, GETS requests are serviced by the owner node, and GETX requests are send to all the sharers. Thus only nodes holding tokens are accessed and broadcast avoided, which reduce network traffic. Experiment results show that overall, for TF256 and TF1024, the interconnect traffic is reduced by average of 34.3% and 27.9% respectively, the endpoint traffic is reduced by average of 32.6% and 26.7%respectively. Our experimentation also shows that TF256 performs better than TF1024 for some applications.