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- Issa, Shady, et al.
(författare)
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Green-CM : Energy efficient contention management for Transactional Memory
- 2015
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Ingår i: <em>44th International Conference on Parallel Processing (ICPP)</em>, September 2015. - : IEEE.
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Konferensbidrag (refereegranskat)abstract
- Transactional memory (TM) is emerging as an attractive synchronization mechanism for concurrent computing. In this work we aim at filling a relevant gap in the TM literature, by investigating the issue of energy efficiency for one crucial building block of TM systems: contention management. Green-CM, the solution proposed in this paper, is the first contention management scheme explicitly designed to jointly optimize both performance and energy consumption. To this end Green-TM combines three key mechanisms: i) it leverages on a novel asymmetric design, which combines different backoff policies in order to take advantage of dynamic frequency and voltage scaling; ii) it introduces an energy efficient design of the back-off mechanism, which combines spin-based and sleep-based implementations; iii) it makes extensive use of selftuning mechanisms to pursue optimal efficiency across highly heterogeneous workloads. We evaluate Green-CM from both the energy and performance perspectives, and show that it can achieve enhanced efficiency by up to 2.35 times with respect to state of the art contention managers, with an average gain of more than 60% when using 64 threads.
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| 3. |
- Issa, Shady, 1989-
(författare)
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Techniques for Enhancing the Efficiency of Transactional Memory Systems
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transactional Memory (TM) is an emerging programming paradigm that drastically simplifies the development of concurrent applications by relieving programmers from a major source of complexity: how to ensure correct, yet efficient, synchronization of concurrent accesses to shared memory. Despite the large body of research devoted to this area, existing TM systems still suffer from severe limitations that hamper both their performance and energy efficiency.This dissertation tackles the problem of how to build efficient implementations of the TM abstraction by introducing innovative techniques that address three crucial limitations of existing TM systems by: (i) extending the effective capacity of Hardware TM (HTM) implementations; (ii) reducing the synchronization overheads in Hybrid TM (HyTM) systems; (iii) enhancing the efficiency of TM applications via energy-aware contention management schemes.The first contribution of this dissertation, named POWER8-TM (P8TM), addresses what is arguably one of the most compelling limitations of existing HTM implementations: the inability to process transactions whose footprint exceeds the capacity of the processor's cache. By leveraging, in an innovative way, two hardware features provided by IBM POWER8 processors, namely Rollback-only Transactions and Suspend/Resume, P8TM can achieve up to 7x performance gains in workloads that stress the capacity limitations of HTM.The second contribution is Dynamic Memory Partitioning-TM (DMP-TM), a novel Hybrid TM (HyTM) that offloads the cost of detecting conflicts between HTM and Software TM (STM) to off-the-shelf operating system memory protection mechanisms. DMP-TM's design is agnostic to the STM algorithm and has the key advantage of allowing for integrating, in an efficient way, highly scalable STM implementations that would, otherwise, demand expensive instrumentation of the HTM path. This allows DMP-TM to achieve up to 20x speedups compared to state of the art HyTM solutions in uncontended workloads.The third contribution, Green-CM, is an energy-aware Contention Manager (CM) that has two main innovative aspects: (i) a novel asymmetric design, which combines different back-off policies in order to take advantage of Dynamic Frequency and Voltage Scaling (DVFS) hardware capabilities, available in most modern processors; (ii) an energy efficient implementation of a fundamental building block for many CM implementations, namely, the mechanism used to back-off threads for a predefined amount of time. Thanks to its innovative design, Green-CM can reduce the Energy Delay Product by up to 2.35x with respect to state of the art CMs.All the techniques proposed in this dissertation share an important common feature that is essential to preserve the ease of use of the TM abstraction: the reliance on on-line self-tuning mechanisms that ensure robust performance even in presence of heterogeneous workloads, without requiring prior knowledge of the target workloads or architecture.
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| 4. |
- Jung, Christian, et al.
(författare)
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A comparison of very old patients admitted to intensive care unit after acute versus elective surgery or intervention
- 2019
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Ingår i: Journal of critical care. - : W B SAUNDERS CO-ELSEVIER INC. - 0883-9441 .- 1557-8615. ; 52, s. 141-148
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Tidskriftsartikel (refereegranskat)abstract
- Background: We aimed to evaluate differences in outcome between patients admitted to intensive care unit (ICU) after elective versus acute surgery in a multinational cohort of very old patients (80 years; VIP). Predictors of mortality, with special emphasis on frailty, were assessed.Methods: In total, 5063 VIPs were induded in this analysis, 922 were admitted after elective surgery or intervention, 4141 acutely, with 402 after acute surgery. Differences were calculated using Mann-Whitney-U test and Wilcoxon test. Univariate and multivariable logistic regression were used to assess associations with mortality.Results: Compared patients admitted after acute surgery, patients admitted after elective surgery suffered less often from frailty as defined as CFS (28% vs 46%; p < 0.001), evidenced lower SOFA scores (4 +/- 5 vs 7 +/- 7; p < 0.001). Presence of frailty (CFS >4) was associated with significantly increased mortality both in elective surgery patients (7% vs 12%; p = 0.01), in acute surgery (7% vs 12%; p = 0.02).Conclusions: VIPs admitted to ICU after elective surgery evidenced favorable outcome over patients after acute surgery even after correction for relevant confounders. Frailty might be used to guide clinicians in risk stratification in both patients admitted after elective and acute surgery.
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| 5. |
- Lacagnina, Giovanni, 1982-, et al.
(författare)
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PIV investigations on optical magnification and small scales in the near-field of an orifice jet
- 2015
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Ingår i: Experiments in Fluids. - : Springer. - 0723-4864 .- 1432-1114. ; 56
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Tidskriftsartikel (refereegranskat)abstract
- Among turbulent jets, the orifice jet is still far from being fully understood especially due to the phenomenon of “vena contracta”, which takes place in the near field. In this work, the attention is focused to large-scale statistics (mean field and higher statistical moments of the velocity) and to small-scale statistics (velocity derivative statistical moments) of such a jet, with a special focus onto the effect of optical magnification on particle image velocimetry measurements. In order to investigate this effect on the measurements, framed areas of different size have been considered by changing the magnification factor through the object plane distance. The obtained results show that a limit on the choice of this parameter exists for a proper description of both small and large scales.
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