Experiences with Disjoint Data Structures in a New Hardware Transactional Memory System

In this paper we present our experiences constructing and testing in-memory data structures designed to be disjoint enough for transactional memory to be profitable as a serialization mechanism with no fallback to traditional locking. Our goal was to restrict memory conflicts to actual contention situations so that transactional memory techniques could be used as efficiently as possible. We describe the hardware transactional execution facility in the IBM zEnterprise EC12 server. We present an order preserving hashed structure that permits insertion, deletion, and traversal operations typically supported by a sorted linked list. We measure the performance and scalability for these operations on the IBM zEnterprise EC12 server. Our results show near linear scalability of the insertion and deletion operations for up to 96 CPUs. We also discuss transaction abort frequency and hardware/software interactions.