Performance degradation in parallel-server systems with shared resources and lack of coordination

E. Hyytiä and R. Righter, “Performance degradation in parallel-server systems with shared resources and lack of coordination,” Performance Evaluation, to appear, 2021. (Extended version of the Valuetools paper) https://doi.org/10.1016/j.peva.2021.102260

Abstract. Parallel server systems are ubiquitous. Multicore CPUs are in practically every personal device from mobile handsets to high-end desktop PCs. At larger scale, data centers consist of a huge number of physical servers often shared by multiple users (for economic reasons). Moreover, the simultaneous users are typically unaware of each other due to reasons that can be technical (cf. security & privacy), practical (coordination layer would add complexity) and business related (usage can be business sensitive information). The workload patterns of different users may also vary significantly. This results in unpredictable and often long response times. We study means for tackling these challenges. In particular, we consider a model where multiple users (dispatchers) route their jobs to a pool of servers using uncoordinated static dispatching policies. The goal is to determine how different policies interact: whether users’ decisions support each other, or if some decisions are simply counterproductive. The lack of proper coordination is shown to increase the mean response times, with two common and robust dispatching policies: Size-Interval-Task Assignment (SITA) and Round-Robin (RR). We refer to this phenomenon as the price of ignorance.