Using Hardware-Transactional-Memory Support to Implement Thread-Level Speculation

Abstract

This paper presents a detailed analysis of the application of Hardware Transactional Memory (HTM) support for loop parallelization with Thread-Level Speculation (TLS) and describes a careful evaluation of the implementation of TLS on the HTM extensions available in such machines. The sample implementation of TLS over HTM described in this paper also provides evidence that the programming effort to implement TLS over HTM support is non-trivial. Thus the paper also describes an extension to OpenMP that both makes TLS more accessible to OpenMP programmers and allows for the easytuning of TLS parameters. As a result, it provides evidence to support several important claims about the performance of TLS over HTM in the Intel Core and the IBM POWER8 architectures. Experimental results reveal that by implementing TLS on top of HTM, speed-ups of up to 3.8x can be obtained for some loops.