Exploring the Limits of Tag Reduction for Energy Saving on a Multi-core Processor

Abstract

Saving energy usually leads to performance degradation. We explore the limits of tag reduction on a multi-core processor with guaranteed performance effect. In our previous work, tag reduction is applied to multi-core processors and shows significant energy savings, meanwhile it causes performance overhead. In this paper, we have found out that when tag reduction is used on multi-core processors, the number of cores is the key factor that affects both energy and performance. More specifically, when tag reduction is applied to multi-core processors, as the number of core integrated into the chip increases, tag reduction can save more energy, while causes more performance degradation. Tag reduction has the limits that are represented by the number of cores. In order to derive the limits, we study the relationship between energy consumption and performance overhead and propose a decision model. We build up an experiment platform that is composed of Linux Physical Memory Monitor (LPMM), Trace Recorder (TR), Scalable Multi-core Simulator (SMS) and Data Analysis Module (DAM). We evaluate benchmarks from SPEC CPU2006 on a real operating system with help of LPMM and TR; and then get the raw results about energy and performance using SMS; finally, DAM analyzes the raw results and finds out the limits. Experimental results show that tag reduction should be applied to the multi-core processor which integrates no more than 6 cores; otherwise, the energy- and performance-efficiency of tag reduction degrades.