The parallel event loop model and runtime: a parallel programming model and runtime system for safe event-based parallel programming

Recent trends in programming models for server-side development have shown an increasing popularity of event-based single- threaded programming models based on the combination of dynamic languages such as JavaScript and event-based runtime systems for asynchronous I/O management such as Node.JS. Reasons for the success of such models are the simplicity of the single-threaded event-based programming model as well as the growing popularity of the Cloud as a deployment platform for Web applications. Unfortunately, the popularity of single-threaded models comes at the price of performance and scalability, as single-threaded event-based models present limitations when parallel processing is needed, and traditional approaches to concurrency such as threads and locks don't play well with event-based systems. This dissertation proposes a programming model and a runtime system to overcome such limitations by enabling single-threaded event-based applications with support for speculative parallel execution. The model, called Parallel Event Loop, has the goal of bringing parallel execution to the domain of single-threaded event-based programming without relaxing the main characteristics of the single-threaded model, and therefore providing developers with the impression of a safe, single-threaded, runtime. Rather than supporting only pure single-threaded programming, however, the parallel event loop can also be used to derive safe, high-level, parallel programming models characterized by a strong compatibility with single-threaded runtimes. We describe three distinct implementations of speculative runtimes enabling the parallel execution of event-based applications. The first implementation we describe is a pessimistic runtime system based on locks to implement speculative parallelization. The second and the third implementations are based on two distinct optimistic runtimes using software transactional memory. Each of the implementations supports the parallelization of applications written using an asynchronous single-threaded programming style, and each of them enables applications to benefit from parallel execution

The parallel event loop model and runtime: a parallel programming model and runtime system for safe event-based parallel programming

Recent trends in programming models for server-side development have shown an increasing popularity of event-based single- threaded programming models based on the combination of dynamic languages such as JavaScript and event-based runtime systems for asynchronous I/O management such as Node.JS. Reasons for the success of such models are the simplicity of the single-threaded event-based programming model as well as the growing popularity of the Cloud as a deployment platform for Web applications. Unfortunately, the popularity of single-threaded models comes at the price of performance and scalability, as single-threaded event-based models present limitations when parallel processing is needed, and traditional approaches to concurrency such as threads and locks don't play well with event-based systems. This dissertation proposes a programming model and a runtime system to overcome such limitations by enabling single-threaded event-based applications with support for speculative parallel execution. The model, called Parallel Event Loop, has the goal of bringing parallel execution to the domain of single-threaded event-based programming without relaxing the main characteristics of the single-threaded model, and therefore providing developers with the impression of a safe, single-threaded, runtime. Rather than supporting only pure single-threaded programming, however, the parallel event loop can also be used to derive safe, high-level, parallel programming models characterized by a strong compatibility with single-threaded runtimes. We describe three distinct implementations of speculative runtimes enabling the parallel execution of event-based applications. The first implementation we describe is a pessimistic runtime system based on locks to implement speculative parallelization. The second and the third implementations are based on two distinct optimistic runtimes using software transactional memory. Each of the implementations supports the parallelization of applications written using an asynchronous single-threaded programming style, and each of them enables applications to benefit from parallel execution

Dynamic web worker pool management for highly parallel javascript web applications

JavaScript web applications are improving performance mainly thanks to the inclusion of new standards by HTML5. Among others, web workers API allows multithreaded JavaScript web apps to exploit parallel processors. However, developers have difficulties to determine the minimum number of web workers that provide the highest performance. But even if developers found out this optimal number, it is a static value configured at the beginning of the execution. Because users tend to execute other applications in background, the estimated number of web workers could be non-optimal, because it may overload or underutilize the system. In this paper, we propose a solution for highly parallel web apps to dynamically adapt the number of running web workers to the actual available resources, avoiding the hassle to estimate a static optimal number of threads. The solution consists in the inclusion of a web worker pool and a simple management algorithm in the web app. Even though there are co-running applications, the results show our approach dynamically enables a number of web workers close to the optimal. Our proposal, which is independent of the web browser, overcomes the lack of knowledge of the underlying processor architecture as well as dynamic resources availability changes.Peer ReviewedPostprint (author's final draft

PyCUDA and PyOpenCL: A Scripting-Based Approach to GPU Run-Time Code Generation

High-performance computing has recently seen a surge of interest in heterogeneous systems, with an emphasis on modern Graphics Processing Units (GPUs). These devices offer tremendous potential for performance and efficiency in important large-scale applications of computational science. However, exploiting this potential can be challenging, as one must adapt to the specialized and rapidly evolving computing environment currently exhibited by GPUs. One way of addressing this challenge is to embrace better techniques and develop tools tailored to their needs. This article presents one simple technique, GPU run-time code generation (RTCG), along with PyCUDA and PyOpenCL, two open-source toolkits that support this technique. In introducing PyCUDA and PyOpenCL, this article proposes the combination of a dynamic, high-level scripting language with the massive performance of a GPU as a compelling two-tiered computing platform, potentially offering significant performance and productivity advantages over conventional single-tier, static systems. The concept of RTCG is simple and easily implemented using existing, robust infrastructure. Nonetheless it is powerful enough to support (and encourage) the creation of custom application-specific tools by its users. The premise of the paper is illustrated by a wide range of examples where the technique has been applied with considerable success.Comment: Submitted to Parallel Computing, Elsevie

Measuring a HTML5 Hybrid Application's Native Bridge on iOS

Mobile apps are intended to be created with mobile platforms development tools and programming languages. This native development requires specialized skills and can therefore be prohibitively expensive. HTML5 hybrid app development is a popular alternative for native mobile app development. This development model allows developers to use standard web technologies and the end result can be indistinguishable from a native app by its visual representation. This model enables faster iteration speed, allows any web developer to build apps and supports simultaneous cross-platform development. However, since the web technology is not as performant as native, these hybrid apps have often been criticized for being noticeably 'laggy' by the app developer community and end users. One of the key components that affects HTML5 hybrid apps performance is the native bridge used in the app. This component bridges the embedded HTML5 application to the device features that wouldn't otherwise be available (such as writing to a file on the device's file system). The native bridge is one of the few components that a developer can freely change. Selecting the best native bridge for the app's needs is important as an inefficient native bridge can cause human noticeable delay in the app. The performance of native bridges has been acknowledged in academia and industry, but very little researched systematically. This thesis introduces a systematic method to evaluate native bridges performance. Along with this method, this thesis also describes a new open source tool implementing this method for benchmarking different native bridges. This tool hosts reference implementation for 32 native bridges. Example results from a test suite that tested all implemented native bridges with two embeddable web view engines (UIWebView and WKWebView) on four distinct iOS devices (two iPads, iPhone and iPod Touch) are evaluated. The results show that the majority of the known native bridge methods can cause human noticeable visual and auditory latency. It is also indicated that the performance is largely affected by app usage patterns. The slowest measured native bridge was over two times slower (from no delay to significant user interface delay) than the fastest one

Performance Evaluation of Job Scheduling and Resource Allocation in Apache Spark

Advancements in data acquisition techniques and devices are revolutionizing the way image data are collected, managed and processed. Devices such as time-lapse cameras and multispectral cameras generate large amount of image data daily. Therefore, there is a clear need for many organizations and researchers to deal with large volume of image data efficiently. On the other hand, Big Data processing on distributed systems such as Apache Spark are gaining popularity in recent years. Apache Spark is a widely used in-memory framework for distributed processing of large datasets on a cluster of inexpensive computers. This thesis proposes using Spark for distributed processing of large amount of image data in a time efficient manner. However, to share cluster resources efficiently, multiple image processing applications submitted to the cluster must be appropriately scheduled by Spark cluster managers to take advantage of all the compute power and storage capacity of the cluster. Spark can run on three cluster managers including Standalone, Mesos and YARN, and provides several configuration parameters that control how resources are allocated and scheduled. Using default settings for these multiple parameters is not enough to efficiently share cluster resources between multiple applications running concurrently. This leads to performance issues and resource underutilization because cluster administrators and users do not know which Spark cluster manager is the right fit for their applications and how the scheduling behaviour and parameter settings of these cluster managers affect the performance of their applications in terms of resource utilization and response times. This thesis parallelized a set of heterogeneous image processing applications including Image Registration, Flower Counter and Image Clustering, and presents extensive comparisons and analyses of running these applications on a large server and a Spark cluster using three different cluster managers for resource allocation, including Standalone, Apache Mesos and Hodoop YARN. In addition, the thesis examined the two different job scheduling and resource allocations modes available in Spark: static and dynamic allocation. Furthermore, the thesis explored the various configurations available on both modes that control speculative execution of tasks, resource size and the number of parallel tasks per job, and explained their impact on image processing applications. The thesis aims to show that using optimal values for these parameters reduces jobs makespan, maximizes cluster utilization, and ensures each application is allocated a fair share of cluster resources in a timely manner

Accelerating interpreted programming languages on GPUs with just-in-time compilation and runtime optimisations

Nowadays, most computer systems are equipped with powerful parallel devices such as Graphics Processing Units (GPUs). They are present in almost every computer system including mobile devices, tablets, desktop computers and servers. These parallel systems have unlocked the possibility for many scientists and companies to process significant amounts of data in shorter time. But the usage of these parallel systems is very challenging due to their programming complexity. The most common programming languages for GPUs, such as OpenCL and CUDA, are created for expert programmers, where developers are required to know hardware details to use GPUs. However, many users of heterogeneous and parallel hardware, such as economists, biologists, physicists or psychologists, are not necessarily expert GPU programmers. They have the need to speed up their applications, which are often written in high-level and dynamic programming languages, such as Java, R or Python. Little work has been done to generate GPU code automatically from these high-level interpreted and dynamic programming languages. This thesis presents a combination of a programming interface and a set of compiler techniques which enable an automatic translation of a subset of Java and R programs into OpenCL to execute on a GPU. The goal is to reduce the programmability and usability gaps between interpreted programming languages and GPUs. The first contribution is an Application Programming Interface (API) for programming heterogeneous and multi-core systems. This API combines ideas from functional programming and algorithmic skeletons to compose and reuse parallel operations. The second contribution is a new OpenCL Just-In-Time (JIT) compiler that automatically translates a subset of the Java bytecode to GPU code. This is combined with a new runtime system that optimises the data management and avoids data transformations between Java and OpenCL. This OpenCL framework and the runtime system achieve speedups of up to 645x compared to Java within 23% slowdown compared to the handwritten native OpenCL code. The third contribution is a new OpenCL JIT compiler for dynamic and interpreted programming languages. While the R language is used in this thesis, the developed techniques are generic for dynamic languages. This JIT compiler uniquely combines a set of existing compiler techniques, such as specialisation and partial evaluation, for OpenCL compilation together with an optimising runtime that compile and execute R code on GPUs. This JIT compiler for the R language achieves speedups of up to 1300x compared to GNU-R and 1.8x slowdown compared to native OpenCL

A Safety-First Approach to Memory Models.

Sequential consistency (SC) is arguably the most intuitive behavior for a shared-memory multithreaded program. It is widely accepted that language-level SC could significantly improve programmability of a multiprocessor system. However, efficiently supporting end-to-end SC remains a challenge as it requires that both compiler and hardware optimizations preserve SC semantics. Current concurrent languages support a relaxed memory model that requires programmers to explicitly annotate all memory accesses that can participate in a data-race ("unsafe" accesses). This requirement allows compiler and hardware to aggressively optimize unannotated accesses, which are assumed to be data-race-free ("safe" accesses), while still preserving SC semantics. However, unannotated data races are easy for programmers to accidentally introduce and are difficult to detect, and in such cases the safety and correctness of programs are significantly compromised. This dissertation argues instead for a safety-first approach, whereby every memory operation is treated as potentially unsafe by the compiler and hardware unless it is proven otherwise. The first solution, DRFx memory model, allows many common compiler and hardware optimizations (potentially SC-violating) on unsafe accesses and uses a runtime support to detect potential SC violations arising from reordering of unsafe accesses. On detecting a potential SC violation, execution is halted before the safety property is compromised. The second solution takes a different approach and preserves SC in both compiler and hardware. Both SC-preserving compiler and hardware are also built on the safety-first approach. All memory accesses are treated as potentially unsafe by the compiler and hardware. SC-preserving hardware relies on different static and dynamic techniques to identify safe accesses. Our results indicate that supporting SC at the language level is not expensive in terms of performance and hardware complexity. The dissertation also explores an extension of this safety-first approach for data-parallel accelerators such as Graphics Processing Units (GPUs). Significant microarchitectural differences between CPU and GPU require rethinking of efficient solutions for preserving SC in GPUs. The proposed solution based on our SC-preserving approach performs nearly on par with the baseline GPU that implements a data-race-free-0 memory model.PhDComputer Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120794/1/ansingh_1.pd

Web page performance analysis

Computer systems play an increasingly crucial and ubiquitous role in human endeavour by carrying out or facilitating tasks and providing information and services. How much work these systems can accomplish, within a certain amount of time, using a certain amount of resources, characterises the systems’ performance, which is a major concern when the systems are planned, designed, implemented, deployed, and evolve. As one of the most popular computer systems, the Web is inevitably scrutinised in terms of performance analysis that deals with its speed, capacity, resource utilisation, and availability. Performance analyses for the Web are normally done from the perspective of the Web servers and the underlying network (the Internet). This research, on the other hand, approaches Web performance analysis from the perspective of Web pages. The performance metric of interest here is response time. Response time is studied as an attribute of Web pages, instead of being considered purely a result of network and server conditions. A framework that consists of measurement, modelling, and monitoring (3Ms) of Web pages that revolves around response time is adopted to support the performance analysis activity. The measurement module enables Web page response time to be measured and is used to support the modelling module, which in turn provides references for the monitoring module. The monitoring module estimates response time. The three modules are used in the software development lifecycle to ensure that developed Web pages deliver at worst satisfactory response time (within a maximum acceptable time), or preferably much better response time, thereby maximising the efficiency of the pages. The framework proposes a systematic way to understand response time as it is related to specific characteristics of Web pages and explains how individual Web page response time can be examined and improved