A Thread Tranquilizer: Dynamically Reducing Performance Variation

To realize the performance potential of multicore systems, we must effectively manage the interactions between memory reference behaviour and the operating system policies for thread scheduling and migration decisions. We observe that these interactions lead to significant variations in the performance of a given application, from one execution to the next, even when the program input remains unchanged and no other applications are being run on the system. Our experiments with multithreaded programs, including the TATP database application, SPECjbb2005, and a subset of PARSEC and SPEC OMP programs, on a 24-core Dell PowerEdge R905 server running OpenSolaris confirms the above observation. In this work we develop Thread Tranquilizer, an automatic technique for simultaneously reducing performance variation and improving performance by dynamically choosing appropriate memory allocation and process scheduling policies. Thread Tranquilizer uses simple utilities available on modern Operating Systems for monitoring cache misses and thread context-switches and then utilizes the collected information to dynamically select appropriate memory allocation and scheduling policies. In our experiments, Thread Tranquilizer yields up to 98% (average 68%) reduction in performance variation and up to 43% (average 15%) improvement in performance over default policies of OpenSolaris. We also demonstrate that Thread Tranquilizer simultaneously reduces performance variation and improves performance of the programs on Linux. Thread Tranquilizer is easy to use as it does not require any changes to the application source code or the OS kernel.