Applications running concurrently on a multicore system interfere with each other at the main memory. This interference can slow down different applications differently. Accurately estimating the slow down of each application in such a system can enable mechanisms that can enforce quality-of-service. While much prior work has focused on mitigating the performance degradation due to inter-application interference, there is little work on estimating slow down of individual applications in a multi-programmed environment. Our goal in this work is to build such an estimation scheme. To this end, we present our simple Memory-Interference-induced Slowdown Estimation (MISE) model that estimates slowdowns caused by memory interference. We build our model based on two observations. First, the performance of a memory-bound application is roughly proportional to the rate at which its memory requests are served, suggesting that request-service-rate can be used as a proxy for performance. Second, when an application's requests are prioritized over all other applications' requests, the application experiences very little interference from other applications. This provides a means for estimating the uninterfered request-service-rate of an application while it is run alongside other applications. Using the above observations, our model estimates the slowdown of an application as the ratio of its uninterfered and interfered request service rates. We propose simple changes to the above model to estimate the slowdown of non-memory-bound applications. We demonstrate the effectiveness of our model by developing two new memory scheduling schemes: 1) one that provides soft quality-of-service guarantees and 2) another that explicitly attempts to minimize maximum slowdown (i.e., unfairness) in the system. Evaluations show that our techniques perform significantly better than state-of-the-art memory scheduling approaches to address the above problems.

DRAM cells store data in the form of charge on a capacitor. This charge leaks off over time, eventually causing data to be lost. To prevent this data loss from occurring, DRAM cells must be periodically refreshed. Unfortunately, DRAM refresh operations waste energy and also degrade system performance by interfering with memory requests. These problems are expected to worsen as DRAM density increases.

Dynamic random-access memory (DRAM) is the building block of modern main memory systems. DRAM cells must be periodically refreshed to prevent loss of data. These refresh operations waste energy and degrade system performance by interfering with memory accesses. The negative effects of DRAM refresh increase as DRAM device capacity increases. Existing DRAM devices refresh all cells at a rate determined by the leakiest cell in the device. However, most DRAM cells can retain data for significantly longer. Therefore, many of these refreshes are unnecessary. In this paper, we propose RAIDR (Retention-Aware Intelligent DRAM Refresh), a low-cost mechanism that can identify and skip unnecessary refreshes using knowledge of cell retention times. Our key idea is to group DRAM rows into retention time bins and apply a different refresh rate to each bin. As a result, rows containing leaky cells are refreshed as frequently as normal, while most rows are refreshed less frequently. RAIDR uses Bloom filters to efficiently implement retention time bins. RAIDR requires no modification to DRAM and minimal modification to the memory controller. In an 8-core system with 32 GB DRAM, RAIDR achieves a 74.6% refresh reduction, an average DRAM power reduction of 16.1%, and an average system performance improvement of 8.6% over existing systems, at a modest storage overhead of 1.25 KB in the memory controller. RAIDR's benefits are robust to variation in DRAM system configuration, and increase as memory capacity increases.