The XOR Cache: A Catalyst for Compression

Modern computing systems allocate significant amounts of resources for caching, especially for the last level cache (LLC). We observe that there is untapped potential for compression by leveraging redundancy due to private caching and inclusion that are common in today's systems. We introduce the XOR Cache to exploit this redundancy via XOR compression. Unlike conventional cache architectures, XOR Cache stores bitwise XOR values of line pairs, halving the number of stored lines via a form of inter-line compression. When combined with other compression schemes, XOR Cache can further boost intra-line compression ratios by XORing lines of similar value, reducing the entropy of the data prior to compression. Evaluation results show that the XOR Cache can save LLC area by 1.93× and power by 1.92× at a cost of 2.06% performance overhead compared to a larger uncompressed cache, reducing energy-delay product by 26.3%.