No More Backstabbing... A Faithful Scheduling Policy for Multithreaded Programs

Efficient contention management is the key to achieving scalable performance for multithreaded applications running on multicore systems. However, contention management policies provided by modern operating systems increase context-switches and lead to performance degradation for multithreaded applications under high loads. Moreover, this problem is exacerbated by the interaction between contention management policies and OS scheduling polices. Time Share (TS) is the default scheduling policy in a modern OS such as Open Solaris and with TS policy, priorities of threads change very frequently for balancing load and providing fairness in scheduling. Due to the frequent ping-ponging of priorities, threads of an application are often preempted by the threads of the same application. This increases the frequency of involuntary context-switches as wells as lock-holder thread preemptions and leads to poor performance. This problem becomes very serious under high loads. To alleviate this problem, in this paper, we present a scheduling policy called Faithful Scheduling (FF), which dramatically reduces context-switches as well as lock-holder thread preemptions. We implemented FF on a 24-core Dell Power Edge R905 server running OpenSolaris.2009.06 and evaluated it using 22 programs including the TATP database application, SPECjbb2005, programs from PARSEC, SPEC OMP, and some micro benchmarks. The experimental results show that FF policy achieves high performance for both lightly and heavily loaded systems. Moreover it does not require any changes to the application source code or the OS kernel.