Directory-Based Conflict Detection in Hardware Transactional Memory

Titos, Rubén; Acacio, Manuel E.; García, José M.

doi:10.1007/978-3-540-89894-8_47

Cited by 4 publications

(2 citation statements)

References 15 publications

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“…A first approximation to the advantages offered by directory-based conflict detection in distributed sharedmemory multiprocessors was presented in [23]. Here, we extend that work with the following contributions:…”

Section: Introductionmentioning

confidence: 88%

Efficient Eager Management of Conflicts for Scalable Hardware Transactional Memory

Titos-Gil

Acacio

Garcia

2013

IEEE Trans. Parallel Distrib. Syst.

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The efficient management of conflicts among concurrent transactions constitutes a key aspect that hardware transactional memory (HTM) systems must achieve. Scalable HTM proposals so far inherit the cache-based style of conflict detection typically found in bus-based systems, largely unaware of the interactions between transactions and directory coherence. In this paper, we demonstrate that the traditional approach of detecting conflicts at the private cache levels is inefficient when used in the context of a directory protocol. We find that the use of the directory as a mere router of coherence requests restricts the throughput of conflict detection, and show how it becomes a bottleneck under high contention. This paper proposes a scheme for conflict detection that decouples conflict detection from cache coherence in order to overcome pathological situations that degrade the performance of an eager HTM system. Our scheme places bookkeeping metadata at the directory, introducing it as a separate hardware module that leaves the coherence protocol unmodified. In comparison to a state-of-the-art eager HTM system, our design handles contention more efficiently, minimizes the performance degradation of false positives for signatures of similar hardware cost, and reduces the network traffic generated.

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Section: Introductionmentioning

confidence: 88%

Efficient Eager Management of Conflicts for Scalable Hardware Transactional Memory

Titos-Gil

Acacio

Garcia

2013

IEEE Trans. Parallel Distrib. Syst.

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“…Nonetheless, encouraging the programmer to use coarse-grain critical sections is a doubleedged sword that may lead to conservative synchronization and create artificially large transactions that increase conflict probability and cause unnecessary conflicts. To this respect, benchmarks composed of coarse-grain transactions have already shown that conflicts can be very frequent [18]. Therefore, within its possibilities, the hardware must do its best to extract parallelism from any given set of concurrent transactions -no matter the number of conflicts that may arise -and it should do so in a completely transparent manner to higher abstraction levels.…”

Section: Introductionmentioning

confidence: 99%

Speculation-based conflict resolution in hardware transactional memory

Titos

Acacio

García

2009

2009 IEEE International Symposium on Parallel &Amp; Distributed Processing

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Conflict management is a key design dimension of hardware transactional memory (HTM) systems, and the implementation of efficient mechanisms for detection and resolution becomes critical when conflicts are not a rare event. Current designs address this problem from two opposite perspectives, namely, lazy and eager schemes. While the former approach is based on an purely optimistic view that is not well-suited when conflicts become frequent, the latter results too pessimistic because resolves conflicts too conservatively, often limiting concurrency unnecessarily. In this paper, we present a hybrid, pseudo-optimistic scheme of conflict resolution for HTM systems that recaptures the concept of speculation to allow transactions to continue their execution past conflicting accesses. Simulation results show that our proposal is capable of combining the advantages of both classical approaches. For the STAMP transactional benchmarks, our hybrid scheme outperforms both eager and lazy systems with average reductions in execution time of 8 and 17%, respectively, and it decreases network traffic by another 17% compared to the eager policy.

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