ReduxSTM: Optimizing STM designs for Irregular Applications

Abstract

The exploitation of optimistic concurrency in modern multicore architectures via Transactional Memory (TM) is becoming a mainstream programming paradigm. TM features can be leveraged to provide support for speculative parallel execution of irregular applications, characterized by a lack of knowledge about data dependences at compile-time. This work is focused on software TM (STM) solutions and how they can be adapted and optimized to deal efficiently with irregular memory access patterns, mainly those caused by reduction operations.With this aim, ReduxSTM is introduced as a specific STM system designed by combining techniques for speculative execution with TM algorithms. ReduxSTM is based on three main design aspects: a transactional commit order mechanism which is available to guarantee sequential semantics when needed; a specific transactional memory primitive defined for expressing commutative and associative operations (reductions) that leverages the underlying TM privatization mechanism to avoid unnecessary transaction aborts caused by reduction memory patterns; and an enhanced conflict resolution mechanism that takes advantage of the two previous features.