Using Silent Writes in Low-Power Traffic-Aware ECC

Abstract: Using Error Detection Code (EDC) and Error Correction Code (ECC) is a noteworthy way to increase cache memories robustness against soft errors. EDC enables detecting errors in cache memory while ECC is used to correct erroneous cache blocks. ECCs are often costly as they impose considerable area and energy overhead on cache memory. Reducing this overhead has been the subject of many studies. In particular, a previous study has suggested mapping ECC to the main memory at the expense of high cache traffic and energy. A major source of this excessive traffic and energy is the high frequency of cache writes. In this work, we show that a significant portion of cache writes are silent, i.e., they write the same data already existing. We build on this observation and introduce Traffic-aware ECC (or simply TCC). TCC detects silent writes by an efficient mechanism. Once such writes are detected updating their ECC is avoided effectively reducing L2 cache traffic and access frequency. Using our solution, we reduce L2 cache access frequency by 8% while maintaining performance. We reduce L2 cache dynamic and overall cache energy by up to 32% and 8%, respectively. Furthermore, TCC reduces L2 cache miss rate by 3%.