Software queue-based algorithms for pipelined synchronization on multiprocessors

Synchronization either ensures mutual exclusion on shared data or forces a processor to wait until a set of variables becomes a specific state; the latter is called conditional synchronization. We have improved the performance of mutual exclusion on multiprocessors by allowing processors to concurrently access different parts of shared data in a pipelined manner (Takesue, 2002). A special software tree of queue-tail pointers is the key scheme for the pipelining, but it requires other hardware schemes such as the queue distributed in the caches. This paper proposes software queue-based algorithms for pipelined synchronization only with the Fetch&Inc. as hardware support. We pipeline mutual exclusion by exploiting the software tree. Conditional synchronization is pipelined by declaring the semaphore as a data structure, and by simulating the P and V operations so that the V can be eagerly performed before accessing shared data. Evaluation results with an RTL (register transfer level) simulator show that as compared with hardware queue-based non-pipelined synchronization, the speedup of our pipelining reaches up to over 2.0 for large data in heavily contentious cases.