AGRAS: Aging and memory request rate aware scheduler for PCM memories

Emerging non-volatile memories overcome the bottlenecks associated with traditional DRAM memories, such as low density and high energy. The high operating voltages required for such non-volatile memories make them vulnerable to Biased Temperature Instability (BTI) aging. The aging of a device can be controlled by the de-stress operation, where the stress voltage applied to the device is removed for a small duration. Performing de-stress in regular intervals helps to partially recover from age degradation. Such an interval-based de-stress can affect the service of regular requests and thus can hamper the system performance.To control the aging of PCM memories while maintaining the system performance, we propose AGRAS: age and memory request-rate aware scheduling method to schedule de-stress as well as regular requests. AGRAS schedules the de-stress operation only when the incoming request rate is not very high, thus controlling performance degradation. Additionally, it makes sure that in events of a prolonged high request rate, the de-stress gets scheduled in order to control device age degradation. The proposal helps to improve the system performance while minimizing the age degradation compared to the setup, which de-stresses at regular intervals.