Abstract: Hardware Transactional Memory (HTM) systems reflect choices from three key design dimensions: conflict detection, version management and conflict resolution. Previously proposed HTMs represent three points in this design space: lazy conflict detection, lazy version management, committer wins (LL); eager conflict detection, lazy version management, requester wins (EL); and eager conflict detection, eager version management, and requester stalls with conservative deadlock avoidance (EE).

To isolate the effects of these high-level design decisions, we develop a common framework that abstracts away differences in cache write policies, interconnects, and ISA to compare these three design points. Not surprisingly, the relative performance of these systems depends on the workload. Under light transactional loads they perform similarly, but under heavy loads they differ by up to 80%. None of the systems performs best on all of our benchmarks.

We identify seven performance pathologies-- interactions between workload and system that degrade performance--as the root cause of many performance differences: FRIENDLYFIRE, STARVINGWRITER, SERIALIZEDCOMMIT, FUTILESTALL, STARVINGELDER, RESTARTCONVOY, and DUELINGUPGRADES. We discuss when and on which systems these pathologies can occur and show that they actually manifest within TM workloads. The insight provided by these pathologies motivated four enhanced systems that often significantly reduce transactional memory overhead. Importantly, by avoiding transaction pathologies, each enhanced system performs well across our suite of benchmarks.

 


BIOGRAPHY:
Prof. David A. Wood is a Professor and Romnes Fellow in the Computer Sciences Department at the University of Wisconsin, Madison. Dr. Wood also holds a courtesy appointment in the Department of Electrical and Computer Engineering. 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. He joined the faculty at the University of Wisconsin in 1990.
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 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, 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 eleven U.S. and International patents.


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 availability, designability, programmability, and performance of commercial multiprocessor and chip multiprocessor servers.