Tribeca: Design for PVT variations with local recovery and fine-grained adaptation

With continued advances in CMOS technology, parameter variations are emerging as a major design challenge. Irregularities during the fabrication of a microprocessor and variations of voltage and temperature during its operation widen worst-case timing margins of the design - degrading performance significantly. Because runtime variations like supply voltage droops and temperature fluctuations depend on the activity signature of the processor´s workload, there are several opportunities to improve performance by dynamically adapting margins. This paper explores the power-performance efficiency gains that result from designing for typical conditions while dynamically tuning frequency and voltage to accommodate the runtime behavior of workloads. Such a design depends on a fail-safe mechanism that allows it to protect against margin violations during adaptation; we evaluate several such mechanisms, and we propose a local recovery scheme that exploits spatial variation among the units of the processor. While a processor designed for worst-case conditions might only be capable of a frequency that is 75% of an ideal processor with no parameter variations, we show that a fine-grained global frequency tuning mechanism improves power-performance efficiency (BIPS³/W) by 40% while operating at 91% of an ideal processor´s frequency. Moreover, a per-unit voltage tuning mechanism aims to reduce the effect of within-die spatial variations to provide a 55% increase in power-performance efficiency. The benefits reported are clearly substantial in light of the <1% area overhead relative to existing global recovery mechanisms.