基于访存局部性的一致性请求广播范围预测

Prediction of Coherence Request Broadcast Range Based on Access Locality

目前广泛采用的广播协议带宽需求较高,目录协议访存延迟较大,不适用于国产服务器处理器片间直连接口带宽相对较低、延迟较高的应用场景。为此,基于片内目录、片间Token广播的双层异构混合一致性协议,应用访存局部性原理,对片间请求广播范围进行预测研究,提出一种HP-SRW协议。实验结果表明,与两级目录协议相比,该协议时间性能提高8.9%,带宽需求降低3.1%,与混合协议相比时间性能略有提升,带宽需求降低30.6%,与Token协议相比,HP-SRW协议以4.7%的时间性能为代价,带宽需求降低66.5%。

Snoopy protocols and directory protocols are widely used in modern server systems,but the former need large bandwidth, directory protocols have long latency, so they are not suitable for domestic server processor where bandwidth is relatively small and latency is relatively long. This paper based on a hybrid coherence protocol which uses Token protocol inter chip and directory protocol intra chip,and uses the access locality to predict the destination of the request. Experimental results show that the HP-SRW protocol has 8.9% better performance than the two-level directory protocol, and 3.1% less demand of bandwidth. It has 30.6% less demand of bandwidth than Hybrid Protocol （HP）. Compared with the Token protocol,the HP-SRW significantly reduces the demand of inter-chip bandwidth by 66.5% at the cost of 4.7% performance.