Improving the reliability of on-chip L2 cache using redundancy

The reliability of large on-chip L2 cache poses a significant challenge due to technology scaling trends. As the minimum feature size continues to decrease, the L2 caches become more vulnerable to multi-bit soft errors. Traditionally, L2 caches have been protected from multi-bit soft errors using techniques like using error detection/correction codes or employing physical interleaving of cache bit lines to convert multi-bit errors into single-bit errors. These methods, however, incur large overheads in area and power. In this work, we investigate several new techniques for reducing multi-bit errors in large L2 caches, in which the multi-bit errors are detected using simple error detection codes and corrected using the data redundancy in the memory hierarchy. Further, we develop a reliability aware replacement policy that dynamically trades performance for reliability whenever the soft-error budget is exceeded. In order to further improve reliability, we propose the duplication of the data values in cache lines by exploiting their small data widths. The proposed techniques were implemented in the Simplescalar framework and validated using the SPEC 2000 integer and floating point benchmarks. The proposed techniques improve the reliability of L2 caches by 40% and 32% on the average, for integer and floating point applications respectively, with little impact on performance and area.