Rethinking Prefetching for Intermittent Computing

Prefetching improves performance by reducing cache misses. However, conventional prefetchers are too aggressive to serve batteryless energy harvesting systems (EHSs) where energy efficiency is the utmost design priority due to weak input energy and the resulting frequent outages. To this end, this paper proposes IPEX, an Intermittence-aware Prefetching EXtension that can be integrated into existing prefetchers on EHSs. IPEX aims to avert useless prefetches by suppressing the prefetching of the cache blocks receiving no hit before their loss on power failure, which would otherwise waste harvested energy. At a proper moment before an upcoming outage, IPEX throttles the prefetch degree to target only those blocks that are likely to be used before the outage. That way IPEX saves energy and spends it on making further execution progress. Experimental results show that on average, IPEX reduces energy consumption by 7.86% (up to 21.64%) and improves performance by 8.96% (up to 23.49%) compared to a conventional prefetcher.