QuakeTM: Parallelizing a complex serial application using transactional memory

Abstract

'Is transactional memory useful?' is the question that cannot be answered until we provide substantial applications that can evaluate its capabilities. While existing TM applications can partially answer the above question, and are useful in the sense that they provide a first-order TM experimentation framework, they serve only as a proof of concept and fail to make a conclusive case for wide adoption by the general computing community. This work presents QuakeTM, a multiplayer game server; a complex real life TM application that was parallelized from the serial version with TM-specific considerations in mind. QuakeTM consists of 27,600 lines of code spread among 49 files and exhibits irregular parallelism and coarse-grain transactions with large read and write sets. In spite of its complexity, we show that QuakeTM does scale, however more effort is needed to decrease the overhead and the abort rate of current software transactional memory systems. We give insights into development challenges, suggest techniques to solve them and provide extensive analysis of transactional behavior of QuakeTM, with an emphasis and discussion of the TM promise of making parallel programming easy.