面向众核负载聚集模式的动态区域化层次一致性协议研究

负载聚集模式给众核处理器结构，尤其是cache一致性协议的设计，带来了诸多挑战。高效一致性协议必须充分利用负载聚集模式的数据共享特性，在虚拟机内部提供低延迟的数据共享，在虚拟机之间提供低开销的数据共享，同时还应支持虚拟机动态迁移和区域隔离。区域化层次一致性协议具备满足这些需求的潜力，但现有设计只关注上层协议层，忽略了底层片上网络，导致它们在延迟、开销和支持虚拟机动态迁移及区域隔离等方面存在较大缺陷。本项目从协同设计一致性协议和片上网络的角度出发，充分利用片上网络的特性设计动态区域化层次一致性协议，在区域内研究监听协议以降低事务延迟，在区域间研究目录协议以优化带宽开销，将在面向负载聚集模式的一致性协议框架、基于无序网络的带宽优化监听协议、低开销低延迟的目录协议、片上网络对聚合通信和区域隔离的硬件支持等方面取得创新研究成果。这些成果可直接用于众核处理器设计，具有重要的理论意义和实用价值。

Workload Consolidation brings several challenges to the design of many-core architecture, especially the cache coherence protocol. An efficient coherence protocol must take full advantage of the data sharing characteristics of workload consolidation; it must provides low latency data sharing within a virtual machine (VM), and supports low cost data sharing between several VMs. Besides, the coherence protocol should allow the VM migration and provide region isolation. The hierarchical coherence protocol with dynamic regions has potential to meet these requirements. Yet, since existing work mainly focuses on protocol-level issues and ignores networks-on-chip (NoCs), it has significant limitations in the latency, cost, the support for VM migration and VM isolation and etc.. .We address these limitations by co-designing the coherence protocol and network-on-chip. We will make full use of the network-on-chip to design efficient hierarchical coherence protocols with dynamic regions. For the protocol maintaining coherence within a VM, we will research snoopy protocols to reduce the transaction latency. For the protocol maintaining coherence between several VMs, we will study directory protocols to reduce the bandwidth cost. We will obtain several innovation outcomes including the coherence protocol framework for workload consolidation, bandwidth efficient snoopy protocols on unordered NoC, low cost and low latency directory protocols, the NoC support for collective communications and region isolation. They could be used directly in current design of many-core platforms, and have important theoretical meanings and practical values.