Using runtime activity to dynamically filter out inefficient data prefetches

International audienceData prefetching is an effective way to bridge the increasing performance gap between processor and memory. Prefetching can improve performance but it has some side effects which may lead to no performance improvement while increasing memory pressure or to performance degradation. Adaptive prefetching aims at reducing negative effects of prefetching while keeping its advantages. This paper proposes an adaptive prefetching method based on runtime activity, which corresponds to the processor and memory activities retrieved by hardware counters, to predict the prefetch efficiency. Our approach highlights and relies on the correlation between the prefetch effects and runtime activity. Our method learns all along the execution this correlation to predict the prefetch efficiency in order to filter out predicted inefficient prefetches. Experimental results show that the proposed filter is able to cancel the negative impact of prefetching when it is unprofitable while keeping the performance improvement due to prefetching when it is beneficial. Our filter works similarly well when several threads are running simultaneously which shows that runtime activity enables an efficient adaptation of prefetch by providing information on running-applications behaviors and interactions