The Performance of Holding Versus Releasing Locks in a Multiprogrammed Multiprocessor

In a multiprogrammed multiprocessor system, existing lock based mechanisms hold the lock for a task during a context-switch. In this case, the time that a task holds a lock can be greatly increased, resulting in a wasted lock utilization and an increase in the average response time for tasks using the lock. An option for avoiding this problem is to release the lock held by a task during a context-switch. The lock is reacquired when the task executes in the next quantum. In this paper, we compare the performance of releasing versus holding a lock during a critical section. We discuss our implementation, the ICSM-R algorithm, as implemented on a multiprocessor system. Next, we develop an analytical performance model, and validate it with a simulation. We study the various parameters under which the ICSM-R algorithm outperforms lock-based algorithms. We nd that if the critical section execution time is 50% or less of the time quantum, ICSM-R has better performance than locking alone, reducing response times and improving scalability.