Energy balance between voltage-frequency scaling and resilience for linear algebra routines on low-power multicore architectures

[EN] Near Threshold Voltage (NTV) computing has been recently proposed as a technique to save energy, at the cost of incurring higher error rates including, among others, Silent Data Corruption (SDC). In this paper, we evaluate the energy efficiency of dense linear algebra routines using several low-power multicore processors and we analyze whether the potential energy reduction achieved when scaling the processor to operate at a low voltage compensates the cost of integrating a fault tolerance mechanism that tackles SDC. Our study targets algorithmic-based fault-tolerant versions of the dense matrix-vector and matrix(matrix) multiplication kernels (GEMV and GEMM, respectively), using the BLIS framework, as well as an implementation of the LU factorization with partial pivoting built on top of GEMM, Furthermore, we tailor the study for a number of representative 32-bit and 64-bit multicore processors from ARM that were specifically designed for energy efficiency. (C) 2017 Elsevier B.V. All rights reserved.The researchers from Universidad Jaume I were supported by project CICYT TIN2014-53495-R of MINECO and FEDER, and the FPU program of MECD. The researcher from Universitat Politecnica de Catalunya was supported by projects TIN2015-65316-P from the Spanish Ministry of Education and 2014 SGR 1051 from the Generalitat de Catalunya, Dep. d'Innovacio, Universitats i Empresa.Catalán, S.; Herrero, JR.; Quintana Ortí, ES.; Rodríguez-Sánchez, R. (2018). Energy balance between voltage-frequency scaling and resilience for linear algebra routines on low-power multicore architectures. Parallel Computing. 73:28-39. https://doi.org/10.1016/j.parco.2017.05.004S28397

Do twins share the same dress code?:Quantifying relative genetic and environmental contributions to subjective perceptions of "the dress" in a classical twin study

The phenomenon of contrasting color perceptions of "the dress" photograph has gained scientific interest. The mechanism underlying why individuals differ is yet to be fully explained. We use the powerful twin model design to ascertain the relative contribution of genetic and environmental factors on perception variation. A sample of 466 twins from the British TwinsUK registry were invited to report what color they saw in a standard image of the dress in standard illumination. The mean age of the participants was 49.5 (SD = 17.8) years, and 85% were female. When asked to choose between white and gold (WG) or blue and black (BB), 328 reported WG (70.4%) and 135 (29.0%) reported BB. Subjects choosing WG were significantly older (p < 0.01), but there was no significant difference in gender. Monozygotic (MZ) twins were more concordant in their responses than dizygotic (DZ) twins (0.46 vs. 0.36). Twin modeling revealed that genetic factors accounted for 34% (95% confidence interval, 5%-59%) of variation in the reported color of the dress when adjusted for age, whereas environmental factors contributed 66% (95% CI, 41%-95%). This study suggests environmental factors play a significant role in how an individual perceives the color of "the dress.

Effect of varying skin surface electrode position on electroretinogram responses recorded using a handheld stimulating and recording system

Purpose A handheld device (the RETeval system, LKC Technologies) aims to increase the ease of electroretinogram (ERG) recording by using specially designed skin electrodes, rather than corneal electrodes. We explored effects of electrode position on response parameters recorded using this device. Methods Healthy adult twins were recruited from the TwinsUK cohort and underwent recording of light-adapted flicker ERGs (corresponding to international standard stimuli). In Group 1, skin electrodes were placed in a “comfortable” position, which was up to 20 mm below the lid margin. For subsequent participants (Group 2), the electrode was positioned 2 mm from the lid margin as recommended by the manufacturer. Amplitudes and peak times (averaged from both eyes) were compared between groups after age-matching and inclusion of only one twin per pair. Light-adapted flicker and flash ERGs were recorded for an additional 10 healthy subjects in two consecutive recording sessions: in the test eye, electrode position was varied from 2 to 10–20 mm below the lid margin between sessions; in the fellow (control) eye, the electrode was 2 mm below the lid margin throughout. Amplitudes and peak times (test eye normalised to control eye) were compared for the two sessions. Results Including one twin per pair, and age-matching yielded 28 individuals per group. Flicker ERG amplitudes were significantly lower for Group 1 than Group 2 participants (p = 0.0024). However, mean peak times did not differ between groups (p = 0.54). For the subjects in whom electrode position was changed between recording sessions, flash and flicker amplitudes were significantly lower when positioned further from the lid margin (p  0.5). Conclusions Moving the skin electrodes further from the lid margin significantly reduces response amplitudes, highlighting the importance of consistent electrode positioning. However, this does not significantly affect peak times. Thus, it may be feasible to adopt a more comfortable position in participants who cannot tolerate the recommended position if analysis is restricted to peak time parameters

Improving Large Scale Application Performance via Data Movement Reduction

The compute capacity growth in high performance computing (HPC) systems is outperforming improvements in other areas of the system for example, memory capacity, network bandwidth and I/O bandwidth. Therefore, the cost of executing a floating point operation is decreasing at a faster rate than moving that data. This increasing performance gap causes wasted CPU cycles while waiting for slower I/O operations to complete in the memory hierarchy, network, and storage. These bottlenecks decrease application time to solution performance, and increase energy consumption, resulting in system under utilization. In other words, data movement is becoming a key concern for future HPC system-design. Data volume reduction techniques (e.g. lossless data compression, information hiding approaches, difference-based patches etc.) have been useful in many contexts to reduce data movement. In this thesis, I study the use of such techniques to reduce data movement in the context of current and future HPC environments. I trade off computation to reduce data volume, for faster completion of I/O operations. I identify three key data movement areas in HPC, intra-process, inter-process and inter-application data movement and investigate the impacts of various compression techniques on the data associated with each of these areas. To be specific, I introduce a compression-based paging system for HPC memory and demonstrate up to 78\% capacity improvement with minimal runtime overhead (4\%). Next, I propose and demonstrate a novel two-level diff-based approach that can reduce inter-process data movement by up to 99\% although with potentially large runtime overhead. Finally, I reduce inter-application data movement by up to 90\% using checkpoint/restart-based fault tolerance protocol as a case study. By doing so, I show that checkpoint data compression can improve application runtime efficiency by more than 50\% and reduce energy expenditure by up to 90\%

Antimony(III)-selenium complexes with synergetic effect between Sb-Se bond and Sb center dot center dot center dot pi interactions

The imidazole-selone antimony(III) complexes have been described with unique bonding situations around the antimony center. The mononuclear complexes, (L-1)SbCl3 (1) and (L-2)SbCl3 (2) were isolated from the reaction between SbCl3 and corresponding symmetrically crowded, 1,3-bis(2,6-diisopropyl phenyl) imidazole selone (L-1) and unsymmetrically crowded, 2,(2,6-benzhydryl-4-methyl phenyl) imidazole pyridine selone (L-2), respectively. The bonding nature of 1 and 2 differ remarkably due to the unique steric hindrance around the antimony center. Besides, the lone-pair-pi-hole interaction was observed in 1 and 2. The extent of Se -{\textgreater} Sb bonding and (aryl)C -{\textgreater} Sb bonding were further investigated by density functional theory (DFT), including natural bond orbital (NBO), natural population analysis (NPA), and electron density difference (EDD) methods. The theoretical predictions are nearly convincing with a single crystal X-ray analysis. The increasing steric bulk of the imidazole-selone from symmetric to unsymmetrical nature was found to greatly influence the donor-acceptor magnitude of Se -{\textgreater} Sb bonding and (aryl)C -{\textgreater} Sb bonding and lone-pair-pi-hole interactions. The L-2 in 2 acts as a good sigma-donor and pi-donor to Sb(III) compare to L-1 in 1