Proceedings.International Conference on Parallel Architectures and Compilation Techniques (2002)
Sept. 22, 2002 to Sept. 25, 2002
Chris Gniady , Carnegie Mellon University
Babak Falsafi , Carnegie Mellon University
This paper proposes SC++lite, a sequentially-consistent system that relaxes memory order speculatively to bridge the performance gap among memory consistency models. Prior proposals to speculatively relax memory order require large custom on-chip storage to maintain a history of speculative processor and memory state while memory order is relaxed. SC++lite uses the memory hierarchy to store the speculative history, providing a scalable path for speculative SC systems across a wide range of applications and system latencies. We use cycle-accurate simulation of shared-memory multiprocessors to show that SC++lite can fully relax memory order while virtually obviating the need for custom on-chip storage. Moreover, while demand for storage increases significantly with larger memory latencies, SC++lite?s ability to relax memory order remains insensitive to memory latency. An SC++lite system can improve performance over a base SC system by 28% with only 2KB of custom storage in a system with 16 processors. In contrast, speculative SC systems with custom storage require 51KB of storage to improve performance by 31% over a base SC system.
C. Gniady and B. Falsafi, "Speculative Sequential Consistency with Little Custom Storage," Proceedings.International Conference on Parallel Architectures and Compilation Techniques(PACT), Charlottesville, Virginia, 2002, pp. 179.