Residue cache: A low-energy low-area L2 cache architecture via compression and partial hits

L2 cache memories are being adopted in the embedded systems for high performance, which, however, increases energy consumption due to their large sizes. We propose a low-energy low-area L2 cache architecture, which performs as well as the conventional L2 cache architecture with 53% less area and around 40% less energy consumption. This architecture consists of an L2 cache and a small cache called residue cache. L2 and residue cache lines are half sized of the conventional L2 cache lines. Well compressed conventional L2 cache lines are stored only in the L2 cache while other poorly compressed lines are stored in both the L2 and residue caches. Although many conventional L2 cache lines are not fully captured by the residue cache, most accesses to them do not incur misses because not all their words are needed immediately, which are termed as partial hits in this paper. The residue cache architecture consumes much lower energy and area than conventional L2 cache architectures, and can be combined synergistically with other schemes such as the line distillation and ZCA. The residue cache architecture is also shown to perform well on a 4-way superscalar processor typically used in high performance systems.