BulkCommit: Scalable and fast commit of atomic blocks in a lazy multiprocessor environment

To help improve the programmability and performance of shared-memory multiprocessors, there are proposals of architectures that continuously execute atomic blocks of instructions - also called Chunks. To be competitive, these architectures must support chunk operations very efficiently. In particular, in a large manycore with lazy conflict detection, they must support efficient chunk commit. This paper addresses the challenge of providing scalable and fast chunk commit for a large manycore in a lazy environment. To understand the problem, we first present a model of chunk commit in a distributed directory protocol. Then, to attain scalable and fast commit, we propose two general techniques: (1) Serialization of the write sets of output-dependent chunks to avoid squashes and (2) Full parallelization of directory module ownership by the committing chunks. Our simulation results with 64-threaded codes show that our combined scheme, called BulkCommit, eliminates most of the squash and commit stall times, speeding-up the codes by an average of 40% and 18% compared to previously-proposed schemes.