Modelling coherence overhead of multi-versioned caches for random accesses

Abstract

Our goal is to predict the performance of multi-node systems consisting of identical processing nodes from single node profiles. The performance of multi-node systems that have coherent caches considerably depends on coherence overhead, which is roughly in direct proportion to the number of transfers of cached copies. We analytically model the number of transfers of cached copies of a data block per write access for random accesses where multi-node systems have multi-versioned coherence mechanisms. Our model aims at helping to predict a baseline performance when closed and/or complex business applications are running, such as clustered databases, the algorithmic behaviours of which are practically impossible to analyse and characteristics of which vary from system to system. To empirically verify our analytical model and show how coherence overhead varies in accordance with parameters, we compared the number of transfers that was predicted by our model and that was counted by a toy simulator of multi-versioned mechanisms.