Transactional memory

About: Transactional memory is a research topic. Over the lifetime, 2365 publications have been published within this topic receiving 60818 citations.

Energy-Performance Tradeoffs in Software Transactional Memory

Abstract: Transactional memory (TM) is a new synchronization mechanism devised to simplify parallel programming, thereby helping programmers to unleash the power of current multicore processors. Although software implementations of TM (STM) have been extensively analyzed in terms of runtime performance, little attention has been paid to an equally important constraint faced by nearly all computer systems: energy consumption. In this work we conduct a comprehensive study of energy and runtime tradeoff sin software transactional memory systems. We characterize the behavior of three state-of-the-art lock-based STM algorithms, along with three different conflict resolution schemes. As a result of this characterization, we propose a DVFS-based technique that can be integrated into the resolution policies so as to improve the energy-delay product (EDP). Experimental results show that our DVFS-enhanced policies are indeed beneficial for applications with high contention levels. Improvements of up to 59% in EDP can be observed in this scenario, with an average EDP reduction of 16% across the STAMP workloads.

BlockChop: dynamic squash elimination for hybrid processor architecture

Abstract: Hybrid processors are HW/SW co-designed processors that leverage blocked-execution, the execution of regions of instructions as atomic blocks, to facilitate aggressive speculative optimization. As we move to a multicore hybrid design, fine grained conflicts for shared data can violate the atomicity requirement of these blocks and lead to expensive squashes and rollbacks. However, as these atomic regions differ from those used in checkpointing and transactional memory systems, the extent of this potentially prohibitive problem remains unclear, and mechanisms to mitigate these squashes dynamically may be critical to enable a highly performant multicore hybrid design. In this work, we investigate how multithreaded applications, both benchmark and commercial workloads, are affected by squashes, and present dynamic mechanisms for mitigating these squashes in hybrid processors. While the current wisdom is that there is not a significant number of squashes for smaller atomic regions, we observe this is not the case for many multithreaded workloads. With region sizes of just 200 – 500 instructions, we observe a performance degradation ranging from 10% to more than 50% for workloads with a mixture of shared reads and writes. By harnessing the unique flexibility provided by the software subsystem of hybrid processor design, we present BlockChop, a framework for dynamically mitigating squashes on multicore hybrid processors. We present a range of squash handling mechanisms leveraging retrials, interpretation, and retranslation, and find that BlockChop is quite effective. Over the current response to exceptions and squashes in a hybrid design, we are able to improve the performance of benchmark and commercial workloads by 1.4x and 1.2x on average for large and small region sizes respectively.

An efficient lock-aware transactional memory implementation

Abstract: Transactional memory (TM) is an emerging concurrency control mechanism that provides a simple and composable programming model. Unfortunately, transactions violate the semantics of mutual exclusion locks when they execute concurrently. Due to the prevalence of locks, transactions must be made lock-aware enabling them to correctly interoperate with locks.We present a lock-aware transactional memory (LATM) system that employs a unique communication method using local knowledge of locks coupled with granularity-based policies. Our system allows higher concurrent throughput than prior systems because it only prevents truly conflicting critical sections from executing concurrently. Furthermore, our system relaxes the prior requirement of transaction isolation when executing conflicting transactional critical sections and instead runs these transactions as irrevocable, improving transaction concurrency. We demonstrate our performance improvements mathematically and empirically.Our system also advances LATM research in terms of program consistency. This is achieved by detecting potential deadlocks at run-time and aborting the programs that contain them. Prior systems break deadlocks, which reveal partially executed critical sections to other threads, thereby violating mutual exclusion. Because our system disallows deadlocks, it does not suffer from mutual exclusion violations, improving program consistency.

TransPlant: A parameterized methodology for generating transactional memory workloads

Abstract: Transactional memory provides a means to bridge the discrepancy between programmer productivity and the difficulty in exploiting thread-level parallelism gains offered by emerging chip multiprocessors. Because the hardware has outpaced the software, there are very few modern multithreaded benchmarks available and even fewer for transactional memory researchers. This hurdle must be overcome for transactional memory research to mature and to gain widespread acceptance. Currently, for performance evaluations, most researchers rely on manually converted lock-based multithreaded workloads or the small group of programs written explicitly for transactional memory. Using converted benchmarks is problematic because they have been tuned so well that they may not be representative of how a programmer will actually use transactional memory. Hand coding stressor benchmarks is unattractive because it is tedious and time consuming. A new parameterized methodology that can automatically generate a program based on the desired high-level program characteristics benefits the transactional memory community. In this work, we propose techniques to generate parameterized transactional memory benchmarks based on a feature set, decoupled from the underlying transactional model. Using principle component analysis, clustering, and raw transactional performance metrics, we show that TransPlant can generate benchmarks with features that lie outside the boundary occupied by these traditional benchmarks. We also show how TransPlant can mimic the behavior of SPLASH-2 and STAMP transactional memory workloads. The program generation methods proposed here will help transactional memory architects select a robust set of programs for quick design evaluations.

Method and system for database system transaction management

Abstract: A method and a system for database system transaction management are provided herein. One aspect provides for annotating via a computing device at least one data object residing on the computing device utilizing at least one transaction tag, the at least one transaction tag being configured to indicate a status of an associated data object; processing at least one database transaction utilizing a transactional memory process, wherein access to the at least one data object is determined based on the status of the at least one data object; and updating the status of the at least one data object responsive to an attempted access of the at least one data object by the at least one database transaction. Other embodiments and aspects are also described herein.