Runtime Slack Creation for Processor Performance Variability using System Scenarios

Abstract

Modern microprocessors contain a variety of mechanisms used to mitigate errors in the logic and memory, referred to as Reliability, Availability, and Serviceability (RAS) techniques. Many of these techniques, such as component disabling, come at a performance cost. With the aggressive downscaling of device dimensions, it is reasonable to expect that chip-wide error rates will intensify in the future and perhaps vary throughout system lifetime. As a result, it is important to reclaim the temporal RAS overheads in a systematic way and enable dependable performance. The current article presents a closed-loop control scheme that actuates processor’s frequency based on detected timing interference to ensure performance dependability. The concepts of slack and deadline vulnerability factor are introduced to support the formulation of a discrete time control problem. Default application timing is derived using the system scenario methodology, the applicability of which is demonstrated through simulations. Additionally, the proposed concept is demonstrated on a real platform and application: a Proportional-Integral-Differential controller, implemented within the application, actuates the Dynamic Voltage and Frequency Scaling (DVFS) framework of the Linux kernel to effectively reclaim temporal overheads injected at runtime. The current article discusses the responsiveness and energy efficiency of the proposed performance dependability scheme. Finally, additional formulation is introduced to predict the upper bound of timing interference that can be absorbed by actuating the DVFS of any processor and is also validated on a representative reduction to practice.