"Endless" Workload Analysis of Large-scale Supercomputers

Modern supercomputers are so large and complex that some of their hardware components inevitably go out of order from time to time. Therefore, supercomputer systems require constant and careful health monitoring, and such control is set up in everyday practice of any large HPC center. But a lot of attention should be also paid to the quality of supercomputer usage, describing how fully and efficiently computational resources are utilized. And this task is still far from being solved, leading to system administrators of most supercomputers knowing very little about the quality of their supercomputer job flow as well as possible ways to improve it. In this paper, we present a looped report system that allows to obtain and analyze information of any level of detail about all important aspects describing the quality of the supercomputer workload, starting from the overall system functioning and up to individual job launches. It provides great flexibility by offering an "endless" number of workload analysis scenarios, which allows to determine root causes of various cases of performance degradation using the same approach. This report system is built upon the previously developed TASC software package, aimed at identifying and analyzing performance issues both at the level of individual parallel applications and the entire supercomputer as a whole

Why do users need to take care of their HPC applications efficiency?

High-performance computing takes a very important place in modern scientific research process. And since all scientists want to solve their problems faster, it is very important to speed up these computations. For these purposes, new algorithms are being developed, new HPC systems appear, etc. However, quite little attention is paid to the efficiency of high-performance computations, which often leads to a vast amount of supercomputer resources being idle. It is vital to change this situation; in particular, it is necessary to show users the importance and necessity of optimizing their applications. One of the main steps in this direction is to help users detect performance issues in their programs, analyze their level of criticality as well as root causes, and eliminate them in order to improve application performance. In this article we describe the research being performed at the Lomonosov Moscow State University aimed at solving this problem. In particular, we analyze the results of supercomputer center users survey, showing their opinion on the efficiency analysis. We also share our vision on the HPC center workflow requirements to support system and applications efficiency analysis. After that, we describe a software tool being developed that allows any supercomputer user to obtain and analyze versatile statistics on performance of his HPC jobs, helping him to detect possible root causes of performance degradation

Driving a Petascale HPC Center with Octoshell Management System

Running any computing center is a complex task. With the growth of scales and costs such tasks become challenges. So the top supercomputer sites, being big in everything, have always required special approaches to manage, to control, and to take care of them. At present, large HPC centers can have a variety of totally diverse systems running together up to millions of components, thousands of users worldwide with the full range of complicated applications. Obviously, tons of data have to be managed in a concerted way to allow such an informational factory functioning. This paper shares the design principles, some implementation details and the roadmap vision regarding the Octoshell HPC center management system, which has been developed and is currently being used in the everyday practice of Lomonosov Moscow State University supercomputer center. This open source system manages Lomonosov and Lomonosov-2 systems with a total of over 5 Pflops peak performance complexes at present, providing multiple tools aimed to tackle most typical workflow tasks both for regular users and system administrators in a single shell

Midterm outcomes of the Ozaki procedure in patients with a bicuspid aortic valve: retrospective single-center, non-randomized, parallel-group study

BACKGROUND: An alternative to plastic surgery on the bicuspid aortic valve (BAV) can be replacement of the leaflets with autopericardium using the Ozaki technique. The procedure is characterized by excellent hemodynamic results in the short and long term in patients with tricuspid aortic valve (TAV). However, the question remains about the long-term results of the procedure and the frequency of reoperations in patients with BAV. OBJECTIVE: To analyze the midterm outcomes of the Ozaki procedure in patients with BAV. MATERIALS AND METHODS: Retrospective single-center, non-randomized, parallel-group study was conducted. Since January 2015 to October 1, 2023, the clinic performed 809 Ozaki procedures. The work included 540 patients with studied midterm and long-term outcomes for up to 5 years. Both isolated aortic valve replacement and combined operations with coronary artery bypass grafting and (or) correction of mitral and tricuspid valve defects were performed. RESULTS: Midterm mortality was 5.7% (n=3) in the group with BAV and 7.3% (n=36) in the group with TAV. Reoperation for aortic regurgitation was required in 16 patients (2.9%): 1 patient (1.9%) in BAV group and 15 (3.3%) in TAV group. Freedom from reoperations in patients with BAV after the Ozaki procedure for up to 5 years was 95.4%, in the group with TAV — 92.6%. The peak gradient on the aortic valve in the group with BAV was 16±7.3, in TAV group— 16.4±10.9. 5 years after surgery, the mean gradient on the aortic valve does not exceed 10 mm Hg. CONCLUSION: The Ozaki operation in patients with BAV is an effective and safe procedure in the midterm follow-up period

Volume-surface barrier discharge in dried air in three-electrode system fed by impulse high voltage with nanosecond rise time

Results of experimental investigation of a volume-surface barrier discharge in a three-electrode system under periodic impulse voltage applied to the surface discharge (SD) electrodes and a d.c. potential applied to an additional third electrode are presented. It is shown that there is a strong influence of polarity and amplitude of the d.c. potential on the direct current “extracted” out of the surface discharge plasma layer by electric field of the third electrode. The amount of charged positive species that constitute the “extracted” current prevails under positive impulse voltage for low values of the negative d.c. potential of the third electrode. The amount of negative species prevails with higher values of the positive d.c. positive of the third electrode

A Laboratory Investigation of the Probable Mechanisms of the Action of an Artificial Thunderstorm Cell on Model Aircraft Radomes

The results of experimental laboratory investigations of possible mechanisms of the impact of lightning and thunderclouds on aircraft radomes and equipment inside them are presented. An artificial thunderstorm cell of negative polarity and model aircraft radomes with lightning diverter strips have been used. Experiments have shown that the discharge processes in a radome model significantly depend on the magnitude of the charge that accumulates on the inner and outer surfaces of the radome shell. It is established that the accumulation of large-magnitude charges of different signs on the outer and/or inner surface of the radome (up to hundreds of µC/m2) shell leads to a multivariance of the mechanisms of development of discharge processes inside the radome model, along its surface, and in the space near it. Significant influence of the “reverse” discharge from the antenna model under the radome on the types of current impulses recorded on the antennas under impact of the artificial thunderstorm cell is established. Peculiarities of the discharge formation in the radome model when using solid and segmented diverter strips for its protection are revealed. Parameters of the current impulses registered on the diverter strips and the antennas have been determined. Based on the conducted research, the possible mechanisms of the impact of thunderclouds and lightning discharges on radio-transparent aircraft radomes and the equipment inside them are considered

Influence of Noisy Environments on Behavior of HPC Applications

Many contemporary HPC systems expose their jobs to substantial amounts of interference, leading to significant run-to-run variation. For example, application runtimes on Theta, a Cray XC40 system at Argonne National Laboratory, vary by up to 70, caused by a mix of node-level and system-level effects, including network and file-system congestion in the presence of concurrently running jobs. This makes performance measurements generally irreproducible, heavily complicating performance analysis and modeling. On noisy systems, performance analysts usually have to repeat performance measurements several times and then apply statistics to capture trends. First, this is expensive and, second, extracting trends from a limited series of experiments is far from trivial, as the noise can follow quite irregular patterns. Attempts to learn from performance data how a program would perform under different execution configurations experience serious perturbation, resulting in models that reflect noise rather than intrinsic application behavior. On the other hand, although noise heavily influences execution time and energy consumption, it does not change the computational effort a program performs. Effort metrics that count how many operations a machine executes on behalf of a program, such as floating-point operations, the exchange of MPI messages, or file reads and writes, remain largely unaffected and—rare non-determinism set aside—reproducible. This paper addresses initial stage of an ExtraNoise project, which is aimed at revealing and tackling key questions of system noise influence on HPC applications

The visibility and stability of GaSe nanoflakes of about 50 layers on SiO2/Si wafers

GaSe nanoflakes on silicon substrates covered by SiO2 films are prepared by mechanical exfoliation from the bulk Bridgman-grown GaSe crystals using a scotch tape. The thickness of SiO2 films on Si substrates providing the highest optical contrast for observation of GaSe flakes is estimated by taking into account the spectral sensitivity of a commercial CMOS camera and broadband visible light illumination. According to our estimations, the optimal SiO2 thickness is ∼126 nm for the visualization of GaSe flakes of 1–3 layers and ∼100 nm for the flakes of 40–70 layers. The obtained nanoflakes are investigated by optical and atomic force microscopy and Raman spectroscopy. The observed spectral positions of the Raman peaks are in agreement with the positions of the peaks known for bulk and nanolayered GaSe samples. It is found that the 50 nm thick flakes are stable but are covered by oxide structures with lateral size about 100 nm and height ∼5 nm after ∼9 months exposure to ambient atmosphere