Techniques for multicore thermal management: Classification and new exploration

Power density continues to increase exponentially with each new technology generation, posing a major challenge for thermal management in modern processors. Much past work has examined microarchitectural policies for reducing total chip power, but these techniques alone are insufficient if not aimed at mitigating individual hotspots. The industry's current trend has been toward multicore architectures, which provide additional opportunities for dynamic thermal management. This paper explores various thermal management techniques that exploit the distributed nature of multicore processors. We classify these techniques in terms of core throttling policy, whether that policy is applied locally to a core or to the processor as a whole, and process migration policies. We use Turandot and a HotSpot-based thermal simulator to simulate a variety of workloads under thermal duress on a 4-core PowerPC™ processor. Using benchmarks from the SPEC 2000 suite we characterize workloads in terms of instruction throughput as well as their effective duty cycles. Among a variety of options we find that distributed control-theoretic DVFS alone improves throughput by 2.5X under our test conditions. Our final design involves a PI-based core thermal controller and an outer control loop to decide process migrations. This policy avoids all thermal emergencies and yields a,u average of 2.6X speedup over the baseline across all workloads.