Title: Decoupled Compressed Caches

David Wood

Tuesday, April 22nd, 12pm-1pm
GHC 7501


In multicore processor systems, last-level caches (LLCs) play a crucial role in reducing system energy by i) filtering out expensive accesses to main memory and ii) reducing the time spent executing in high-power states. Cache compression can increase effective cache capacity and reduce misses, improve performance, and potentially reduce system energy. However, previous compressed cache designs have demonstrated only limited benefits due to internal fragmentation and limited tags.

In this talk, I discuss our work on Decoupled Compressed Caches (DCC), which exploit spatial locality to improve both the performance and energy-efficiency of cache compression. DCC uses decoupled super-blocks and non-contiguous sub-block allocation to decrease tag overhead without increasing internal fragmentation. Non-contiguous sub-blocks also eliminate the need for energy-expensive re-compaction when a block's size changes. Compared to earlier compressed caches, DCC increases normalized effective capacity to a maximum of 4 and an average of 2.2 for a wide range of workloads. A further optimized Co-DCC (Co-Compacted DCC) design improves the average normalized effective capacity to 2.6 by co-compacting the compressed blocks in a super-block. Our simulations show that DCC nearly doubles the benefits of previous compressed caches with similar area overhead. We also demonstrate a practical DCC design based on a recent commercial LLC design.


Prof. David A. Wood has been a Professor in the Computer Sciences and Electrical and Computer Engineering (by courtesy) Departments at the University of Wisconsin, Madison since 1990. Dr. Wood received a B.S. in Electrical Engineering and Computer Science (1981) and a Ph.D. in Computer Science (1990), both at the University of California, Berkeley.

Dr. Wood was named an ACM Fellow (2005) and IEEE Fellow (2004), received the University of Wisconsin's H.I. Romnes Faculty Fellowship (1999) and Vilas Associate (2011), and received the National Science Foundation's Presidential Young Investigator award (1991). Dr. Wood is Area Editor (Computer Systems) of ACM Transactions on Modeling and Computer Simulation, is Associate Editor of ACM Transactions on Architecture and Compiler Optimization, serves as Chair of ACM SIGARCH and ACM Council Representative, served as Program Committee Chairman of ASPLOS-X (2002), and has served on numerous program committees. Dr. Wood is an ACM Fellow, an IEEE Fellow, and a member of the IEEE Computer Society. Dr. Wood has published over 70 technical papers and is an inventor on thirteen U.S. and International patents, several of which have been licensed to industry.

Dr. Wood co-leads the Wisconsin Multifacet project with Prof. Mark Hill (URL http://www.cs.wisc.edu/multifacet) which is exploring techniques for improving the performance and energy efficiency of homogeneous and heterogeneous multiprocessor servers.