Unbounded Transactional Memory

Ananian, C. Scott; Asanović, Krste; Kuszmaul, Bradley C.; Leiserson, Charles E.; Lie, Sean

doi:10.1109/hpca.2005.41

Cited by 325 publications

(260 citation statements)

References 20 publications

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“…The TCC system is also built upon a broadcast network that allows transactions to snoop commit traffic to maintain coherence and detect possible dependence violations (conflicts). Later on, several proposals such as UTM [1] or VTM [9] focus on hardware schemes that provide virtualization of transactions, i.e., support for transactions of unlimited duration, size and nesting depth. Both UTM and VTM monitor the coherence traffic for the transaction's cache lines to determine if another processor is performing a conflicting operation.…”

Section: Motivation and Related Workmentioning

confidence: 99%

Directory-Based Conflict Detection in Hardware Transactional Memory

Titos¹,

Acacio²,

García³

2008

High Performance Computing - HiPC 2008

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Abstract. One of the key design points of any hardware transactional memory (HTM) system is the conflict detection mechanism, and its efficient implementation becomes critical when conflicts are not a rare event. While many contemporary proposals rely on the coherence protocol to carry out conflict detection at the private cache levels, this approach is not optimal for systems that use a directory to maintain coherence over an unordered, scalable network, such as tiled CMPs. In this paper, we present a new scheme of conflict detection for HTM systems, which moves this key mechanism from the private caches to the directory level. We propose a novel transactional book-keeping method and describe how this detection can be carried out more efficiently at the directory. Simulation results show that our approach obtains reductions in execution time between 25 and 55% for transactional benchmarks with a high number of conflicts, with an average improvement over LogTM-SE of 15%.

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Section: Motivation and Related Workmentioning

confidence: 99%

Directory-Based Conflict Detection in Hardware Transactional Memory

Titos¹,

Acacio²,

García³

2008

High Performance Computing - HiPC 2008

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“…Several proposals [1,7,12,20] seek to leverage cache coherence protocols to achieve lightweight hardware transactions. However, these hardware TMs generally fix the conflict detection policy at design time, with eager read-write conflict detection more common than lazy [20].…”

Section: Related Workmentioning

confidence: 99%

Conflict Detection and Validation Strategies for Software Transactional Memory

Spear

Marathe

Scherer

et al. 2006

Lecture Notes in Computer Science

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Abstract. In a software transactional memory (STM) system, conflict detection is the problem of determining when two transactions cannot both safely commit. Validation is the related problem of ensuring that a transaction never views inconsistent data, which might potentially cause a doomed transaction to exhibit irreversible, externally visible side effects. Existing mechanisms for conflict detection vary greatly in their degree of speculation and their relative treatment of read-write and write-write conflicts. Validation, for its part, appears to be a dominant factor-perhaps the dominant factor-in the cost of complex transactions.We present the most comprehensive study to date of conflict detection strategies, characterizing the tradeoffs among them and identifying the ones that perform the best for various types of workload. In the process we introduce a lightweight heuristic mechanism-the global commit counter-that can greatly reduce the cost of validation and of single-threaded execution. The heuristic also allows us to experiment with mixed invalidation, a more opportunistic interleaving of reading and writing transactions. Experimental results on a 16-processor SunFire machine running our RSTM system indicate that the choice of conflict detection strategy can have a dramatic impact on performance, and that the best choice is workload dependent. In workloads whose transactions rarely conflict, the commit counter does little to help (and can even hurt) performance. For less scalable applications, however-those in which STM performance has traditionally been most problematic-it can improve transaction throughput many fold.

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“…Example 1 Unbounded Transactional Memory (UTM), proposed in [2], is a hardware transactional memory (HTM) that eagerly updates the main memory with new values while maintaining copies of old values in a transaction log. The description of UTM is outlined in Section 1.…”

Section: Transactional Memoriesmentioning

confidence: 99%

“…We study whether this is also the case for transactional memories, where we focus on different approaches to transactional memory implementation. Specifically, we consider Transactional Memory Coherence and Consistency (TCC) [9], Unbounded Transactional Memory (UTM) [2], and a general scheme for conflict detection and arbitration [17]. Some of these implementations turn out to be secure with respect to the policy associated to arbitrary access control tables, others turn out to be insecure even for the very simple information flow policy involving two agents H and L with information flow from H to L prohibited.…”

Section: Introductionmentioning

confidence: 99%

Access Control and Information Flow in Transactional Memory

Cohen

Meyden

Zuck

2009

Formal Aspects in Security and Trust

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Abstract. The paper considers the addition of access control to a number of transactional memory implementations, and studies its impact on the information flow security of such systems. Even after the imposition of access control, the Unbounded Transactional Memory due to Ananian et al, and most instances of a general scheme for transactional conflict detection and arbitration due to Scott, are shown to be insecure. This result applies even for a very simple policy prohibiting information flow from a high to a low security domain. The source of the insecurity is identified as the ability of agents to cause aborts of other agents' transactions. A generic implementation is defined, parameterized by a "may-abort" relation that defines which agents may cause aborts of other agents' transactions. This implementation is shown to be secure with respect to an intransitive information flow policy consistent with the access control table and "may-abort" relation. Using this result, Transactional Memory Coherence and Consistency, an implementation due to Hammond et al, is shown to be secure with respect to intransitive information flow policies. Moreover, it is shown how to modify Scott's arbitration policies using the may-abort relation, yielding a class of secure implementations closely related to Scott's scheme.

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Unbounded Transactional Memory

Cited by 325 publications

References 20 publications

Directory-Based Conflict Detection in Hardware Transactional Memory

Directory-Based Conflict Detection in Hardware Transactional Memory

Conflict Detection and Validation Strategies for Software Transactional Memory

Access Control and Information Flow in Transactional Memory

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