AVR: Reducing Memory Traffic with Approximate Value Reconstruction

This paper describes Approximate Value Reconstruction (AVR), an architecture for approximate memory compression. AVR reduces the memory traffic of applications that tolerate approximations in their dataset. Thereby, it utilizes more efficiently the available off-chip bandwidth improving significantly system performance and energy efficiency. AVR compresses memory blocks using low latency downsampling that exploits similarities between neighboring values and achieves aggressive compression ratios, up to 16:1 in our implementation. The proposed AVR architecture supports our compression scheme maximizing its effect and minimizing its overheads by (i) co-locating in the Last Level Cache (LLC) compressed and uncompressed data, (ii) efficiently handling LLC evictions, (iii) keeping track of badly compressed memory blocks, and (iv) avoiding LLC pollution with unwanted decompressed data. For applications that tolerate aggressive approximation in large fractions of their data, AVR reduces memory traffic by up to 70%, execution time by up to 55%, and energy costs by up to 20% introducing up to 1.2% error to the application output.