Remote Core Locking: Migrating Critical-Section Execution to Improve the Performance of Multithreaded Applications

National audienceThe scalability of multithreaded applications on current multicore systems is hampered by the performance of lock algorithms, due to the costs of access contention and cache misses. In this paper, we propose a new lock algorithm, Remote Core Locking (RCL), that aims to improve the performance of critical sections in legacy applications on multicore architectures. The idea of RCL is to replace lock acquisitions by optimized remote procedure calls to a dedicated server core. RCL limits the performance collapse observed with other lock algorithms when many threads try to acquire a lock concurrently and removes the need to transfer lock-protected shared data to the core acquiring the lock because such data can typically remain in the server core's cache. We have developed a profiler that identifies the locks that are the bottlenecks in multithreaded applications and that can thus benefit from RCL, and a reengineering tool that transforms POSIX locks into RCL locks. We have evaluated our approach on 18 applications: Memcached, Berkeley DB, the 9 applications of the SPLASH-2 benchmark suite and the 7 applications of the Phoenix2 benchmark suite. 10 of these applications, including Memcached and Berkeley DB, are unable to scale because of locks, and benefit from RCL. Using RCL locks, we get performance improvements of up to 2.6 times with respect to POSIX locks on Memcached, and up to 14 times with respect to Berkeley DB