Intermittence-Aware Cache Compression

Cache compressions are proven effective in improving the performance of caches in conventional processors. They compress data into a smaller size, allowing caches to accommodate more blocks. This helps reduce cache misses and expensive memory accesses, ultimately improving performance. However, conventional cache compression is less effective for energy harvesting systems (EHSs) which experience frequent power failure, as many compressed blocks end up not being used before their loss upon power outage. This wastes hard-won energy, which would otherwise be used for making more program progress. To address this issue, this paper introduces Kagura, an adaptive cache compression extension with frequent power failure in mind. Specifically, Kagura disables cache compression when it finds out that many cached blocks are unlikely to be reused before the next power outage. That way, Kagura avoids the energy waste on useless compressions/decompressions, and the resulting speedup is on par with the ideal intermittence-aware cache compressor. Experimental results show that when combined with an existing cache compressor, Kagura reduces the total energy consumption by an average of 4.53% (up to 16.21%) and improves the performance by an average of 4.74% (up to 17.87%) compared to the baseline EHS without cache compression.