Phase-based tuning: better utilized performance asymmetric multicores

The latest trend towards performance asymmetry among cores on a single chip of a multicore processor is posing new challenges. For effective utilization of these performance-asymmetric multicore processors, code sections of a program must be assigned to cores such that the resource needs of code sections closely matches resource availability at the assigned core. Determining this assignment manually is tedious, error prone, and significantly complicates software development. To solve this problem, this thesis describes a transparent and fully-automatic process called phase-based tuning which adapts an application to effectively utilize performance-asymmetric multicores. The basic idea behind this technique is to statically compute groups of program segments which are expected to behave similarly at runtime. Then, at runtime, the behavior of a few code segments is used to infer the behavior and preferred core assignment of all similar code segments with low overhead. Compared to the stock Linux scheduler, for systems asymmetric with respect to clock frequency, a 36% average process speedup is observed, while maintaining fairness and with negligible overheads. A key component to phase-based tuning is grouping program segments with similar behavior. The importance of various similarity metrics are likely to differ for each target asymmetric multicore processor. Determining groups using too many metrics may result in a grouping that differentiates between program segments based on irrelevant properties for a target machine. Using too few metrics may cause relevant metrics to be ignored thereby considering segments with different behavior similar. Therefore, to solve this problem and enable phase-based tuning for a wide range of a performance-asymmetric multicores, this thesis also describes a new technique called lazy grouping. Lazy grouping statically (at compile and install times) groups program segments that are expected to have similar behavior. The basic idea is to use extensive compile time analysis with intelligent install time (when the target system is known) group assignment. The accuracy of lazy grouping for a wide range of machines is shown to be more than 90% for nearly all target machines and asymmetric multicores

Evaluation of the Dynamic Behavior of Steel Staircases with Concrete Filled Pan Treads

Vibration serviceability of staircases has been a growing challenge for structural engineers due to changing materials and structural forms. In order to prevent or correct serviceability problems due to structural vibrations, structural engineers should be able to predict the dynamic performance of a staircase structure. However, there are few technical guides available for designing steel staircases, and the ones that do exist are often limited in their applications. Currently, there is a lack of research on staircases that are less prone to vibrations, such as staircases with concrete filled pans that are composed of face and wall stringers. Therefore, the goal of this thesis is to improve the understanding and accuracy of the overall vibration response (natural frequencies and mode shapes) predictions of concrete filled pan tread stairs. In order to determine the vibration response, experimental data was collected on two types of staircases and used to create and update finite element models. Using the experimentally updated finite element models, various parameters such as railing mass and boundary conditions were altered, demonstrating the staircases’ response to changes in these parameters. This study also demonstrated different methods for modeling the unknown boundary condition stiffness contributions in the staircase structure. In addition, this thesis evaluated the potential limitations of the AISC design guide equation that quickly calculates a prediction of the first mode frequency of a staircase. This thesis also suggested an empirical factor to be applied to the AISC equation that would allow the equation to be used for staircases with a boundary condition created by a wall stringer. Finally, this thesis work has created suggestions for designers on how to model these types of staircases. Advisors: Ece Erdogmus and Jay Pucket

Phase-based tuning for better utilized performance-asymmetric multicores

The latest trend towards performance asymmetry among cores on a single chip of a multicore processor is posing new software engineering challenges for developers. A key challenge is that for effective utilization of these performance-asymmetric multicore processors, application threads must be assigned to cores such that the resource needs of a thread closely matches resource availability at the assigned core. Determining this assignment manually is tedious, error prone, and it significantly complicates software development. We contribute a transparent and fully-automatic program analysis, which we call phase-guided tuning, to solve this problem. Phase-guided tuning adapts an application to effectively utilize performance-asymmetric cores of a processor. Our technique does not require any changes in the compiler or operating system, thus it is easy to deploy in existing tool chains. It does not require any input from the programmer except the application. Furthermore, it is independent of the characteristics (performance-asymmetry) of the target multicore processor, which has two benefits. First, it avoids the need to create multiple customizations of the binary for each target architecture, and second it relieves the programmer of the burden of anticipating the target architecture. Last but not least, our technique significantly improves performance. Compared to the stock Linux scheduler, our best technique shows 215% improvement in throughput and 36% average process speedup, while maintaining fairness and with negligible overheads

ParaSCAN: A Static Profiler to Help Parallelization

Parallelizing software often starts by profiling to identify program paths that are worth parallelizing. Static profiling techniques, e.g. hot paths, can be used to identify parallelism opportunities for programs that lack representative inputs and in situations where dynamic techniques aren\u27t applicable, e.g. parallelizing compilers and refactoring tools. Existing static techniques for identification of hot paths rely on path frequencies. Relying on path frequencies alone isn\u27t sufficient for identifying parallelism opportunities. We propose a novel automated approach for static profiling that combines both path frequencies and computational weight of the paths. We apply our technique called ParaSCAN to parallelism recommendation, where it is highly effective. Our results demonstrate that ParaSCAN\u27s recommendations cover all the parallelism manually identified by experts with 85% accuracy and in some cases also identifies parallelism missed by the experts

Frances: A Tool for Understanding Computer Architecture and Assembly Language

Students in all areas of computing require knowledge of the computing device including software implementation at the machine level. Several courses in computer science curricula address these low-level details such as computer architecture and assembly languages. For such courses, there are advantages to studying real architectures instead of simplified examples. However, real architectures and instruction sets introduce complexity that makes them difficult to grasp in a single semester course. Visualization techniques can help ease this burden, unfortunately existing tools are often difficult to use and consequently difficult to adopt in a course where time is already limited. To solve this problem, we present Frances. Frances graphically illustrates key differences between familiar high-level languages and unfamiliar low-level languages and also illustrates how familiar high-level programs behave on real architectures. Key to this tool is that we use a simple Web interface that requires no setup, easing course adoption hurdles. We also include several features that further enhance its usefulness in a classroom setting. These features include graphical relationships between high-level code and machine code, clearly illustrated step-by-step machine state transitions, color coding to make instruction behavior clear, and illustration of pointers. We have used Frances in courses and performed experimental evaluation. Our experiences with Frances in the classroom demonstrate its usability. Most notably, in our experimental setting, students with no computer architecture course experience were able to complete lessons using Frances with no guidance

Evaluation of the Dynamic Behavior of Steel Staircases with Concrete Filled Pan Treads

Vibration serviceability of staircases has been a growing challenge for structural engineers due to changing materials and structural forms. In order to prevent or correct serviceability problems due to structural vibrations, structural engineers should be able to predict the dynamic performance of a staircase structure. However, there are few technical guides available for designing steel staircases, and the ones that do exist are often limited in their applications. Currently, there is a lack of research on staircases that are less prone to vibrations, such as staircases with concrete filled pans that are composed of face and wall stringers. Therefore, the goal of this thesis is to improve the understanding and accuracy of the overall vibration response (natural frequencies and mode shapes) predictions of concrete filled pan tread stairs. In order to determine the vibration response, experimental data was collected on two types of staircases and used to create and update finite element models. Using the experimentally updated finite element models, various parameters such as railing mass and boundary conditions were altered, demonstrating the staircases’ response to changes in these parameters. This study also demonstrated different methods for modeling the unknown boundary condition stiffness contributions in the staircase structure. In addition, this thesis evaluated the potential limitations of the AISC design guide equation that quickly calculates a prediction of the first mode frequency of a staircase. This thesis also suggested an empirical factor to be applied to the AISC equation that would allow the equation to be used for staircases with a boundary condition created by a wall stringer. Finally, this thesis work has created suggestions for designers on how to model these types of staircases. Advisors: Ece Erdogmus and Jay Pucket

Designing an Experimental Setup for Testing Concrete to Steel Bond Transfer with and without Flexure

The purpose of this thesis is to present an experiment design to investigate the steel-concrete interaction exhibited in steel pile jackets. Concrete jackets are a common fix for corroding piles in Nebraska, to restore capacity and prevent further deterioration in the presence of the state’s soil. The experiment design is developed to complement previous research performed at the University of Nebraska-Lincoln. This thesis will cover a series of four tests that are intended to strategically isolate key mechanical behavior to allow for the effects induced by flexure to be distinguished from the effects present without flexure. These tests are strategically designed to improve understanding of how flexure produces enhanced composite effectiveness of bond that is expected when a moment acts in combination with an axial load. Therefore, it is expected that composite effectiveness will be increased (greater load transfer between steel and concrete) as a result of friction induced by steel flexure reacting against the surrounding concrete. Test 1 is designed to quantify the shear transfer available, on an area basis, from chemical cohesion between steel and concrete. Test 2 is designed to investigate end bearing strength, particularly in comparison to code-based design expectations. Test 3 is designed to be a combination of Test 1 and Test 2, and will provide data for combined end bearing and the bond, resulting from chemical cohesion when a pile is subjected to axial load only. Test 3 will provide a reference for Test 4, which includes a flexure loading component. Test 4 will be similar to Test 3, but Test 4 will include moment induced by eccentricity between the centroidal axis of the test specimen and the line of action of applied external axial loads. Experiments performed using the configurations described in this thesis will yield data that will help to further the understanding of the composite effectiveness that occurs when flexure is induced in a pile retrofit scenario, and therefore an improved understanding of the capacity available from this type of retrofit