Energy Efficiency of Software Transactional Memory in a Heterogeneous Architecture

Hardware vendors make an important effort creating low-power CPUs that keep battery duration and durability above acceptable levels. In order to achieve this goal and provide good performance-energy for a wide variety of applications, ARM designed the big.LITTLE architecture. This heterogeneous multi-core architecture features two different types of cores: big cores oriented to performance and little cores, slower and aimed to save energy consumption. As all the cores have access to the same memory, multi-threaded applications must resort to some mutual exclusion mechanism to coordinate the access to shared data by the concurrent threads. Transactional Memory (TM) represents an optimistic approach for shared-memory synchronization. To take full advantage of the features offered by software TM, but also benefit from the characteristics of the heterogeneous big.LITTLE architectures, our focus is to propose TM solutions that take into account the power/performance requirements of the application and what it is offered by the architecture. In order to understand the current state-of-the-art and obtain useful information for future power-aware software TM solutions, we have performed an analysis of a popular TM library running on top of an ARM big.LITTLE processor. Experiments show, in general, better scalability for the LITTLE cores for most of the applications except for one, which requires the computing performance that the big cores offer.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Towards a Software Transactional Memory for heterogeneous CPU-GPU processors

The heterogeneous Accelerated Processing Units (APUs) integrate a multi-core CPU and a GPU within the same chip. Modern APUs provide the programmer with platform atomics, used to communicate the CPU cores with the GPU using simple atomic datatypes. However, ensuring consistency for complex data types is a task delegated to programmers, who have to implement a mutual exclusion mechanism. Transactional Memory (TM) is an optimistic approach to implement mutual exclusion. With TM, shared data can be accessed by multiple computing threads speculatively, but changes are only visible if a transaction ends with no conflict with others in its memory accesses. TM has been studied and implemented in software and hardware for both CPU and GPU platforms, but an integrated solution has not been provided for APU processors. In this paper we present APUTM, a software TM designed to work on heterogeneous APU processors. The design of APUTM focuses on minimizing the access to shared metadata in order to reduce the communication overhead via expensive platform atomics. The main objective of APUTM is to help us understand the tradeoffs of implementing a sofware TM on an heterogeneous CPU-GPU platform and to identify the key aspects to be considered in each device. In our experiments, we compare the adaptability of APUTM to execute in one of the devices (CPU or GPU) or in both of them simultaneously. These experiments show that APUTM is able to outperform sequential execution of the applications.This work has been supported by projects TIN2013-42253-P and TIN2016-80920-R, from the Spanish Government, P11-TIC8144 and P12- TIC1470, from Junta de Andalucía, and Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Improvements in Hardware Transactional Memory for GPU Architectures

In the multi-core CPU world, transactional memory (TM)has emerged as an alternative to lock-based programming for thread synchronization. Recent research proposes the use of TM in GPU architectures, where a high number of computing threads, organized in SIMT fashion, requires an effective synchronization method. In contrast to CPUs, GPUs offer two memory spaces: global memory and local memory. The local memory space serves as a shared scratch-pad for a subset of the computing threads, and it is used by programmers to speed-up their applications thanks to its low latency. Prior work from the authors proposed a lightweight hardware TM (HTM) support based in the local memory, modifying the SIMT execution model and adding a conflict detection mechanism. An efficient implementation of these features is key in order to provide an effective synchronization mechanism at the local memory level. After a quick description of the main features of our HTM design for GPU local memory, in this work we gather together a number of proposals designed with the aim of improving those mechanisms with high impact on performance. Firstly, the SIMT execution model is modified to increase the parallelism of the application when transactions must be serialized in order to make forward progress. Secondly, the conflict detection mechanism is optimized depending on application characteristics, such us the read/write sets, the probability of conflict between transactions and the existence of read-only transactions. As these features can be present in hardware simultaneously, it is a task of the compiler and runtime to determine which ones are more important for a given application. This work includes a discussion on the analysis to be done in order to choose the best configuration solution.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The sharpness of some results on stable solutions of −Δu=f(u) in RN

AbstractIn this note we give a complete answer to a question raised by Dupaigne and Farina (2009) [8] related to the existence of nonconstant stable solutions of the equation −Δu=f(u) in RN, where N≤9 and f is a very general non-negative, non-decreasing and convex nonlinearity

Hardware support for Local Memory Transactions on GPU Architectures

Graphics Processing Units (GPUs) are popular hardware accelerators for data-parallel applications, enabling the execution of thousands of threads in a Single Instruction - Multiple Thread (SIMT) fashion. However, the SIMT execution model is not efficient when code includes critical sections to protect the access to data shared by the running threads. In addition, GPUs offer two shared spaces to the threads, local memory and global memory. Typical solutions to thread synchronization include the use of atomics to implement locks, the serialization of the execution of the critical section, or delegating the execution of the critical section to the host CPU, leading to suboptimal performance. In the multi-core CPU world, transactional memory (TM) was proposed as an alternative to locks to coordinate concurrent threads. Some solutions for GPUs started to appear in the literature. In contrast to these earlier proposals, our approach is to design hardware support for TM in two levels. The first level is a fast and lightweight solution for coordinating threads that share the local memory, while the second level coordinates threads through the global memory. In this paper we present GPU-LocalTM as a hardware TM (HTM) support for the first level. GPU-LocalTM offers simple conflict detection and version management mechanisms that minimize the hardware resources required for its implementation. For the workloads studied, GPU-LocalTM provides between 1.25-80X speedup over serialized critical sections, while the overhead introduced by transaction management is lower than 20%.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Evaluación de metales pesados en aguas residuales descargadas en El Rio Tixcuco, Ciudad de San Miguel

RESUMEN: La investigación Evaluación de metales pesados en aguas residuales descargadas en el rio Tixcuco, ciudad de San Miguel. Se realizó con el objetivo de evaluar los metales pesados en aguas residuales descargadas en el río Tixcuco, ciudad de San Miguel. Se hicieron dos muestreos en época seca en Colonia las Águilas, se recogió agua del rio que fue envasada, preservada y traslada hacia el Laboratorio Físico Químico de Aguas de la Facultad de Química y Farmacia de la Universidad de El Salvador para su respectivo análisis. Se evaluaron las concentraciones de cuatro metales pesados Cadmio (Cd), Plomo (Pb), Mercurio (Hg) y Arsénico (As) por muestra. Para el Cd, Pb y Hg se aplicó en método fotométrico y el As método calorimétrico. Los resultados obtenidos en la primera muestra fueron: As 0.02mg/L,Cd 0.013mg /L,Hg 0.04 mg/L y Pb 0.78mg/L y en la segunda: As 0.2mg/L, Cd. no se realizó por falta de reactivo, Hg no detectado y Pb 0.754mg/L. Los resultados obtenidos se compararon con los valores en el Reglamento Técnico Salvadoreño RTS 13.05.01:18 Agua. Aguas Residuales. El metal pesado que sobrepasa la norma en los dos muestreos es el Plomo ya que según la norma su valor es 0.5mg/l, pero esa diferencia no es significativa y el As sobrepasa en un muestreo. Cuando se realizó la investigación se determinó que las aguas del rio Tixcuco están contaminadas por la presencia de Pb y As, metales que afectan la calidad del agua, la flora y fauna del río y sirve como vehículo de trasmisión de enfermedades a otras especies cercanas al cuerpo de agua. Aunque el Cd y Hg no sobrepasaron la norma, pero hay presencia de ellos que un futuro podrían aumentar su concentración si no descontamina el río y por la coloración del agua presenta gran turbidez. ABSTRAC: The investigation Evaluation of heavy metals in wastewater discharged in the Tixcuco river, city of San Miguel. It was carried out with the objective of evaluating heavy metals in wastewater discharged into the Tixcuco River, city of San Miguel. Two samples were taken in the dry season in Colonia las Águilas, water was collected from the river that was bottled, preserved and transferred to the Physical Chemical Water Laboratory of the Faculty of Chemistry and Pharmacy of the University of El Salvador (UES) for its respective analysis. The concentrations of four heavy metals Cadmium (Cd), Lead (Pb), Mercury (Hg) and Arsenic (As) were evaluated per sample. For Cd, Pb and Hg, the photometric method was applied, and the calorimetric method was used for As. The results obtained in the first sample were: As 0.02mg/L, Cd 0.013mg/L, Hg 0.04 mg/L and Pb 0.78mg/L and in the second: As 0.2mg/L, Cd. was not carried out due to lack of reagent, Hg not detected and Pb 0.754mg/L. The results obtained were compared with the values in the Salvadoran Technical Regulation RTS 13.05.01:18 Water. Sewage water. The heavy metal that exceeds the standard in both samples is Lead since according to the standard its value is 0.5mg/l, but this difference is not significant and As exceeds in one sampling. When the investigation was carried out, it was determined that the waters of the Tixcuco River are contaminated by the presence of Pb and As, metals that affect the quality of the water, the flora and fauna of the river and serve as a vehicle for transmitting diseases to other species near the river. Water body. Although Cd and Hg did not exceed the norm, there is a presence of them that could increase their concentration in the future if it does not decontaminate the river and due to the color of the water it presents great turbidity

Monte Carlo simulation of damage and amorphization induced by swift-ion irradiation in LiNbO3

This paper presents a Monte Carlo (MC) simulation tool which is applied to describe the ion beam induced damage generated by electronic excitation in LiNbO3. Based on a previously published thermal spike based analytical model, the MC technique allows for a more flexible and accurate treatment of the problem. A main advantage of this approach with respect to the analytical one is the possibility of studying the role of statistical fluctuations, relevant at low fluences. The paper recalls the main features of the physical model, describes the MC algorithm, and compares simulation results to experimental data (irradiations of LiNbO3 using silicon ions at 5 and 7.5 MeV and oxygen ions at 5 MeV). © 2006 American Institute of Physics.Peer Reviewe