Compression architecture for bit-write reduction in non-volatile memory technologies

摘要

In this thesis we explore a novel method for improving the performance and lifetime of non-volatile memory technologies. As the development of new DRAM technology reaches physical scaling limits, research into new non-volatile memory technologies has advanced in search of a possible replacement. However, many of these new technologies have inherent problems such as low endurance, long latency, or high dynamic energy. This thesis proposes a simple compression-based technique to improve the performance of write operations in non-volatile memories by reducing the number of bit-writes performed during write accesses. The proposed architecture, which is integrated into the memory controller, relies on a compression engine to reduce the size of each word before it is written to the memory array. It then employs a comparator to determine which bits require write operations. By reducing the number of bit-writes, these elements are capable of reducing the energy consumed, improving throughput, and increasing endurance of non-volatile memories. We examine two different compression methods for compressing each word in our architecture. First, we explore Frequent Value Compression (FVC), which maintains a dictionary of the words used most frequently by the application. We also use a Huffman Coding scheme to perform the compression of these most frequent values. Second, we explore Frequent Pattern Compression (FPC), which compresses each word based on a set of patterns. While this method is not capable of reducing the size of each word as well as FVC, it is capable of compressing a greater number of values. Finally, we implement an intra-word wear leveling method that is able to enhance memory endurance by reducing the peak bit-writes per cell. This method conditionally writes compressed words to separate portions of the non-volatile memory word in order to spread writes throughout each word. Trace-based simulations of the SPEC CPU2006 benchmarks show a 20x reduction in raw bit-writes, which corresponds to a 2-3x improvement over the state-of-the-art methods and a 27% reduction in peak cell bit-writes, improving NVM lifetime.