Abstract-Recently introduced processors such as Tilera's Tile Gx100 and Intel's 48-core SCC have delivered on the promise of high performance per watt in manycore processors, making these architectures ostensibly as attractive for low-power embedded processors as for cloud services. However, these architectures space-multiplex the microarchitectural resources between many threads to increase utilization, which leads to potentially large and varying levels of interference. This decorrelates CPU-time from actual application progress and decreases the ability of traditional software to accurately track and finely control application progress, hindering the adoption of manycore processors in embedded computing.In this paper we propose Progress Time as the counterpart of CPU-time in space-multiplexed systems and show how it can be used to track application progress. We also introduce TimeCube, a manycore embedded processor that uses dynamic execution isolation and shadow performance modeling to provide an accurate online measurement of each application's Progress Time. Our evaluation shows that a 32-core TimeCube processor can track application progress with less than 1% error even in the presence of a 6× average worst-case slowdown. TimeCube also uses Progress Times to perform online architectural resource management that leads to a 36% improvement in throughput compared to existing microarchitectural resource allocation schemes. Overall, the results argue for adding the requisite microarchitectural structures to support Progress Time in manycore chips for embedded systems.
Abstract-In order to increase utilization, multicore processors share memory resources among an increasing number of cores. This sharing leads to memory interference, which in turn leads to a non-uniform degradation in the execution of concurrent applications, even in the presence of fairness mechanisms. Many utilities rely on application CPU Time both for measuring resource usage and inferring application progress. These utilities are therefore directly affected by the distorting effects of multicore interference on the representativeness of CPU Time as a proxy for progress. This makes reasoning about myriad properties from fairness, to QoS, to throughput optimality very difficult in consolidated environments, such as IaaS.We introduce the notion of Quality Time, which provides a measure of application progress analogous to CPU Time's measure of resource usage, and we propose a simple online sampling-based technique to approximate Quality Time with high accuracy. We have implemented three user-space tools called Qtime, Qtop, and Qplacer. Qtime can attach to an application to calculate its Quality Time online, Qtop is a dashboard that monitors the Quality Times of all applications on the system, and Qplacer leverages Quality Time information to find better application placements and improve overall system quality. With Quality Time, we are able to reduce the error in inferring execution efficiency from 150.3% to 25.1% in the worst case and from 30.0% to 7.5% on average. Qplacer can increase average system throughput by 3.2% when compared to static application placement.
Multicore processors have become ubiquitous across many domains, such as datacenters and smartphones. As the number of processing elements increases within these processors, so does the pressure to share the critical on-chip cache resources, but this must be done energy-efficiently and without sacrificing resource guarantees. We propose a scalable dynamic cache-partitioning scheme, DR-SNUCA, which provides an energy-efficient way to reduce resource interference over caches shared among many processing elements. Our results show that DR-SNUCA reduces system energy consumption by 16.3% compared to associatively partitioned caches, such as DNUCA.
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