DStress: Automatic Synthesis of DRAM Reliability Stress Viruses using Genetic Algorithms

Failures become inevitable in DRAM devices, which is a major obstacle for scaling down the density of cells in future DRAM technologies. These failures can be detected by specific DRAM tests that implement the data and memory access patterns having a strong impact on DRAM reliability. However, the design of such tests is very challenging, especially for testing DRAM devices in operation, due to an extremely large number of possible cell-to-cell interference effects and combinations of patterns inducing these effects.In this paper, we present a new framework for the synthesis of DRAM reliability stress viruses, DStress. This framework automatically searches for the data and memory access patterns that induce the worst-case DRAM error behavior regardless the internal DRAM design. The search engine of our framework is based on Genetic Algorithms (GA) and a programming tool that we use to specify the patterns examined by GA. To evaluate the effect of program viruses on DRAM reliability, we integrate DStress with an experimental server where 72 DRAM chips can operate under various operating parameters and temperatures.We present the results of our 7-month experimental study on the search of DRAM reliability stress viruses. We show that DStress finds the worst-case data pattern virus and the worst-case memory access virus with probabilities of 1 - 4 × 10
^-7
and 0.95, respectively. We demonstrate that the discovered patterns induce by at least 45% more errors than the traditional data pattern micro-benchmarks used in previous studies. We show that DStress enables us to detect the marginal DRAM operating parameters reducing the DRAM power by 17.7 % on average without compromising reliability. Overall, our framework facilitates the exploration of new data patterns and memory access scenarios increasing the probability of DRAM errors, which is essential for improving the state-of-the-art DRAM testing mechanisms.