Bubble budgeting: throughput optimization for dynamic workloads by exploiting dark cores in many core systems

All the cores of a many-core chip cannot be active at the same time, due to reasons like low CPU utilization in server systems and limited power budget in dark silicon era. These free cores (referred to as bubbles) can be placed near active cores for heat dissipation so that the active cores can run at a higher frequency level, boosting the performance of active cores and applications. Budgeting inactive cores (bubbles) to workloads to boost performance has the following three challenges. First, the number of bubbles varies due to dynamic workloads. Second, communication distance increases when a bubble is inserted between two communicating tasks, leading to performance degradation. Third, budgeting too many bubbles as cooler to running applications leads to insufficient cores for future applications. In order to address these challenges, in this paper, a bubble budgeting scheme is proposed to budget free cores to each application so as to optimize the throughput of the whole system, including the execution time of each application and the waiting time incurred for newly arrived applications. Essentially, the proposed algorithm determines the number and locations of bubbles to optimize the performance and waiting time of each application, followed by tasks of each application being mapped to a core region. Experiments show that our approach achieves 50% higher throughput when compared to state-of-the-art thermal-aware runtime task mapping approaches.