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Hierarchical Power Management for Asymmetric Multi-Core in Dark Silicon Era. Thannirmalai Somu Muthukaruppan Mihai Pricopi Vanchinathan Venkataramani , Tulika Mitra School of Computing, National University of Singapore Sanjay Vishin Cambridge Silicon Radio DAC’13. Motivation.
Hierarchical Power Management for Asymmetric Multi-Core in Dark Silicon Era ThannirmalaiSomuMuthukaruppan MihaiPricopi VanchinathanVenkataramani, TulikaMitra School of Computing, National University of Singapore Sanjay Vishin Cambridge Silicon Radio DAC’13
Motivation • Dark silicon phenomenon • A chip can have many cores but a significant fraction of them are left un-powered, or dark, at any point in time due to power and thermal limits. • Asymmetric multi-core architecture as an alternative • Cores with diverse power-performance characteristics.
This paper • Introduce a hierarchical power management framework for asymmetric multi-cores. • Builds on control theory. • Coordinates multiple controllers in a synergistic manner to achieve optimal power-performance efficiency. • Respects the thermal design power budget.
Scenario • System exceeds the Thermal Design Power(TDP). • => power budgets have to be reduced. • => scaling down voltage and frequency. • => the QoS degrades. • Reverse the process once the system load decreases. • Avoid oscillations!
ARM big.LITTLE • TC2 • Two high performance Cortex A15 and three energy-efficient Cortex A7 • 3rd model(HMP) • Per-cluster DVFS
Heart Rate • The throughput of the critical kernel of a QoS task. • Ex: number of frames per second(fps) for a video encoder. • Heartbeats in QoS benchmark • Heart rate = heartbeats per second
Feedback Based Controller • Proportional-Integral-Derivative(PID)Controller • Kp, Ki, Kd: proportion, integral, derivative gain.
Resource Share Controller • Target heart rate hrref(Qi) = [hrrefmin,hrrefmax] • Measured heart rate hr(Qi) • Slice s(Qi)
Core Utilization • u(Qi), u(NQj): utilization of ofQoS and non-QoS tasks. • u(Ck) = Σu(Qi) + Σu(NQj): utilization of core k • u(Clm) = max(u(Ck)) : utilization of cluster m
DVFS Controller • Target utilization uref(Clm) = max(uideal, utarget(Clm))
Chip-Level Power Allocator • Hrthrottle(Qi): throttle factor of heart rate.
QoS Controller • Ideal Heart Rate hrideal(Qi) = [hridealmin,hridealmax] • Target Heart Rate hrref(Qi) = [hrrefmin,hrrefmax] = hrideal(Qi) x hrthrottle(Qi)
Load Balancer and Migrator • Balancer ensures that the cores within a cluster are evenly load balanced. • Migrator migrates tasks between clusters.
Experimental Setting • Versatile Express Development Platform • 2 A15 + 3 A7 • Linux Completely Fair Scheduler(CFS) • Benchmarks:
Asymmetric V.S. Symmetric • x264 benchmark • Phases with varying performance requirements during execution.
Conclusion • The authors present a power management framework for asymmetric multi-cores that based on multiple controllers. • Exploits asymmetry among the cores through selective migration and employs DVFS to minimize power consumption while satisfying QoS constraints.