Joint use of OpenMP and MPI technologies on the nodes of the computational cluster

This work is devoted to the problem of implementing an efficient parallel program that solves the asigned task using the maximum available amount of computing cluster resources in order to obtain the corresponding gain in performance with respect to the sequential version of the algorithm. The main objective of the work was to study the possibilities of joint use of the parallelization technologies OpenMP and MPI, considering the characteristics and features of the problems being solved, to increase the performance of executing parallel algorithms and programs on a computing cluster. This article provides a brief overview of approaches to calculating the sequential programs complexity functions. To determine the parallel programs complexity, an approach based on operational analysis was used. The features of the sequential programs parallelization technologies OpenMP and MPI are described. The main software and hardware factors affecting the execution speed of parallel programs on the nodes of a computing cluster are presented. The main attention in this paper is paid to the study of the impact on performance of computational and exchange operations number ratio in programs. To implement the research, parallel OpenMP and MPI testing programs were developed, in which the total number of operations and the correlation between computational and exchange operations are set. A computing cluster consisting of several nodes was used as a hardware and software platform. Experimental studies have made it possible to confirm the effectiveness of the hybrid model of a parallel program in multi-node systems with heterogeneous memory using OpenMP in shared memory subsystems, and MPI in a distributed memory subsystems

EFFICACY OF COGNITIVE TRAINING FOCUSED ON DIFFERENT MEMORY SUBSYSTEMS FOR COMMUNITY DWELLING ELDERLY INDIVIDUALS

Background: With the aging process, some memory subsystems as the episodic and working memory change. Cognitive training has been suggested for prevention of cognitive decline but previous studies have conflicting results. Objective: To verify the efficacy of two types of multidimensional cognitive training programs, one focusing on internal strategies to boost episodic memory (EMT) and another based on activities targeting speed processing and working memory (WMT). Methods: One hundred thirty six community dwelling older adults (aged 60 or over and living independently) took part in the study, 76 undertook EMT, 30 undertook WMT and 30 participated in a control program that focused on autobiographical memory (AMT). Training occurred during 8 weekly group sessions of 1,5h. All groups participated in lectures about cognition and aging during the training. They received activities to practice at home. A neuropsychological battery was applied before and after the interventions. Results: ANOVA of repeated measures pointed to significant higher scores in global cognition (ACER), their memory subtest, and in recall score of categorized noun pictures. The interaction showed that the episodic group improved more than the others in the recall of pictures (interaction between group and task p <0,01). Conclusion: The results demonstrated immediate gains after training in specific episodic memory trained skills.

Implications of NVM Based Storage on Memory Subsystem Management

Recently, non-volatile memory (NVM) has advanced as a fast storage medium, and legacy memory subsystems optimized for DRAM (dynamic random access memory) and HDD (hard disk drive) hierarchies need to be revisited. In this article, we explore the memory subsystems that use NVM as an underlying storage device and discuss the challenges and implications of such systems. As storage performance becomes close to DRAM performance, existing memory configurations and I/O (input/output) mechanisms should be reassessed. This article explores the performance of systems with NVM based storage emulated by the RAMDisk under various configurations. Through our measurement study, we make the following findings. (1) We can decrease the main memory size without performance penalties when NVM storage is adopted instead of HDD. (2) For buffer caching to be effective, judicious management techniques like admission control are necessary. (3) Prefetching is not effective in NVM storage. (4) The effect of synchronous I/O and direct I/O in NVM storage is less significant than that in HDD storage. (5) Performance degradation due to the contention of multi-threads is less severe in NVM based storage than in HDD. Based on these observations, we discuss a new PC configuration consisting of small memory and fast storage in comparison with a traditional PC consisting of large memory and slow storage. We show that this new memory-storage configuration can be an alternative solution for ever-growing memory demands and the limited density of DRAM memory. We anticipate that our results will provide directions in system software development in the presence of ever-faster storage devices.

The role of executive functions and working memory subsystems in the formation of the mental set

The present paper investigates the problem of mechanisms of the development of the effect of mental set, which is at the core of the processes of the implicit learning, development of the experience and solving creative tasks. As such mechanisms we investigate the change of the parameters of functioning of executive control and working memory subsystems. As a result of an experimental study, based on modified tasks by A. Luchins, it was found that mechanisms of the development of the effect of mental set have a systematic nature and include such factors as the change of the parameters of the executive functions and the specifics of the processing and storage of information in modality-specific blocks of the working memory. The role of the executive control is dual: it is necessary for keeping in the sphere of the attention the operations during their automatization, and at the same it, it makes the automatized scheme conscient by destructing the developed effect of the mental set. The executive control plays a role of the element which sets the structure of mechanisms of the development and overcoming of the mental set effect. Processes which proceed during the information processing in working memory subsystems also play an important role in the development of the mental set effect, however their nature requires supplementary research.