Remote Invalidation: Optimizing the Critical Path of Memory Transactions

Software Transactional Memory (STM) systems are increasingly emerging as a promising alternative to traditional locking algorithms for implementing generic concurrent applications. To achieve generality, STM systems incur overheads to the normal sequential execution path, including those due to spin locking, validation (or invalidation), and commit/abort routines. We propose a new STM algorithm called Remote Invalidation (or RInval) that reduces these overheads and improves STM performance. RInval's main idea is to execute commit and invalidation routines on remote server threads that run on dedicated cores, and use cache-aligned communication between application's transactional threads and the server routines. By remote execution of commit and invalidation routines and cache-aligned communication, RInval reduces the overhead of spin locking and cache misses on shared locks. By running commit and invalidation on separate cores, they become independent of each other, increasing commit concurrency. We implemented RInval in the Rochester STM framework. Our experimental studies on micro-benchmarks and the STAMP benchmark reveal that RInval outperforms InvalSTM, the corresponding non-remote invalidation algorithm, by as much as an order of magnitude. Additionally, RInval obtains competitive performance to validation-based STM algorithms such as NOrec, yielding up to 2x performance improvement.