Automatic creation of tile size selection models using neural networks

2010 Spring.Includes bibliographic references (pages 54-59).Covers not scanned.Print version deaccessioned 2022.Tiling is a widely used loop transformation for exposing/exploiting parallelism and data locality. Effective use of tiling requires selection and tuning of the tile sizes. This is usually achieved by hand-crafting tile size selection (TSS) models that characterize the performance of the tiled program as a function of tile sizes. The best tile sizes are selected by either directly using the TSS model or by using the TSS model together with an empirical search. Hand-crafting accurate TSS models is hard, and adapting them to different architecture/compiler, or even keeping them up-to-date with respect to the evolution of a single compiler is often just as hard. Instead of hand-crafting TSS models, can we automatically learn or create them? In this paper, we show that for a specific class of programs fairly accurate TSS models can be automatically created by using a combination of simple program features, synthetic kernels, and standard machine learning techniques. The automatic TSS model generation scheme can also be directly used for adapting the model and/or keeping it up-to-date. We evaluate our scheme on six different architecture-compiler combinations (chosen from three different architectures and four different compilers). The models learned by our method have consistently shown near-optimal performance (within 5% of the optimal on average) across the tested architecture-compiler combinations

Using Decision Tree Voting to Select a Polyhedral Model Loop Transformation

Algorithms in fields like image manipulation, sound and signal processing, and statistics frequently employ tight loops. These loops are computationally intensive and CPU-bound, making their performance highly dependent on efficient utilization of the CPU pipeline and memory bus. Recent years have seen CPU pipelines becoming more and more complicated, with features such as branch prediction and speculative execution. At the same time, clock speeds have stopped their prior exponential growth rate due to heat dissipation issues, and multiple cores have become prevalent. These developments have made it more difficult for developers to reason about how their code executes on the CPU, which in turn makes it difficult to write performant code. An automated method to take code and optimize it for most efficient execution would, therefore, be desirable. The Polyhedral Model allows the generation of alternative transformations for a loop nest that are semantically equivalent to the original. The transformations vary the degree of loop tiling, loop fusion, loop unrolling, parallelism, and vectorization. However, selecting the transformation that would most efficiently utilize the architecture remains challenging. Previous work utilizes regression models to select a transformation, using as features hardware performance counter values collected during a sample run of the program being optimized. Due to inaccuracies in the resulting regression model, the transformation selected by the model as the best transformation often yields unsatisfactory performance. As a result, previous work resorts to using a five-shot technique, which entails running the top five transformations suggested by the model and selecting the best one based on their actual runtime. However, for long-running benchmarks, five runs may be take an excessive amount of time. I present a variation on the previous approach which does not need to resort to the five-shot selection process to achieve performance comparable to the best five-shot results reported in previous work. With the transformations in the search space ranked in reverse runtime order, the transformation selected by my classifier is, on average, in the 86th percentile. There are several key contributing factors to the performance improvements attained by my method: formulating the problem as a classification problem rather than a regression problem, using static features in addition to dynamic performance counter features, performing feature selection, and using ensemble methods to boost the performance of the classifier. Decision trees are constructed from pairs of features (performance counters and structural features than can be determined statically from the source code). The trees are then evaluated according to the number of benchmarks for which they select a transformation that performs better than two baseline variants, the original program and the expected runtime if a randomly selected transformation were applied. The top 20 trees vote to select a final transformation

Performance Analysis and Optimization of Sparse Matrix-Vector Multiplication on Modern Multi- and Many-Core Processors

This paper presents a low-overhead optimizer for the ubiquitous sparse matrix-vector multiplication (SpMV) kernel. Architectural diversity among different processors together with structural diversity among different sparse matrices lead to bottleneck diversity. This justifies an SpMV optimizer that is both matrix- and architecture-adaptive through runtime specialization. To this direction, we present an approach that first identifies the performance bottlenecks of SpMV for a given sparse matrix on the target platform either through profiling or by matrix property inspection, and then selects suitable optimizations to tackle those bottlenecks. Our optimization pool is based on the widely used Compressed Sparse Row (CSR) sparse matrix storage format and has low preprocessing overheads, making our overall approach practical even in cases where fast decision making and optimization setup is required. We evaluate our optimizer on three x86-based computing platforms and demonstrate that it is able to distinguish and appropriately optimize SpMV for the majority of matrices in a representative test suite, leading to significant speedups over the CSR and Inspector-Executor CSR SpMV kernels available in the latest release of the Intel MKL library.Comment: 10 pages, 7 figures, ICPP 201

Representation learning on complex data

Machine learning has enabled remarkable progress in various fields of research and application in recent years. The primary objective of machine learning consists of developing algorithms that can learn and improve through observation and experience. Machine learning algorithms learn from data, which may exhibit various forms of complexity, which pose fundamental challenges. In this thesis, we address two major types of data complexity: First, data is often inherently connected and can be modeled by a single or multiple graphs. Machine learning methods could potentially exploit these connections, for instance, to find groups of similar users in a social network for targeted marketing or to predict functional properties of proteins for drug design. Secondly, data is often high-dimensional, for instance, due to a large number of recorded features or induced by a quadratic pixel grid on images. Classical machine learning methods perennially fail when exposed to high-dimensional data as several key assumptions cease to be satisfied. Therefore, a major challenge associated with machine learning on graphs and high-dimensional data is to derive meaningful representations of this data, which allow models to learn effectively. In contrast to conventional manual feature engineering methods, representation learning aims at automatically learning data representations that are particularly suitable for a specific task at hand. Driven by a rapidly increasing availability of data, these methods have celebrated tremendous success for tasks such as object detection in images and speech recognition. However, there is still a considerable amount of research work to be done to fully leverage such techniques for learning on graphs and high-dimensional data. In this thesis, we address the problem of learning meaningful representations for highly-effective machine learning on complex data, in particular, graph data and high-dimensional data. Additionally, most of our proposed methods are highly scalable, allowing them to learn from massive amounts of data. While we address a wide range of general learning problems with different modes of supervision, ranging from unsupervised problems on unlabeled data to (semi-)-supervised learning on annotated data sets, we evaluate our models on specific tasks from fields such as social network analysis, information security, and computer vision. The first part of this thesis addresses representation learning on graphs. While existing graph neural network models commonly perform synchronous message passing between nodes and thus struggle with long-range dependencies and efficiency issues, our first proposed method performs fast asynchronous message passing and, therefore, supports adaptive and efficient learning and additionally scales to large graphs. Another contribution consists of a novel graph-based approach to malware detection and classification based on network traffic. While existing methods classify individual network flows between two endpoints, our algorithm collects all traffic in a monitored network within a specific time frame and builds a communication graph, which is then classified using a novel graph neural network model. The developed model can be generally applied to further graph classification or anomaly detection tasks. Two further contributions challenge a common assumption made by graph learning methods, termed homophily, which states that nodes with similar properties are usually closely connected in the graph. To this end, we develop a method that predicts node-level properties leveraging the distribution of class labels appearing in the neighborhood of the respective node. That allows our model to learn general relations between a node and its neighbors, which are not limited to homophily. Another proposed method specifically models structural similarity between nodes to model different roles, for instance, influencers and followers in a social network. In particular, we develop an unsupervised algorithm for deriving node descriptors based on how nodes spread probability mass to their neighbors and aggregate these descriptors to represent entire graphs. The second part of this thesis addresses representation learning on high-dimensional data. Specifically, we consider the problem of clustering high-dimensional data, such as images, texts, or gene expression profiles. Classical clustering algorithms struggle with this type of data since it can usually not be assumed that data objects will be similar w.r.t. all attributes, but only within a particular subspace of the full-dimensional ambient space. Subspace clustering is an approach to clustering high-dimensional data based on this assumption. While there already exist powerful neural network-based subspace clustering methods, these methods commonly suffer from scalability issues and lack a theoretical foundation. To this end, we propose a novel metric learning approach to subspace clustering, which can provably recover linear subspaces under suitable assumptions and, at the same time, tremendously reduces the required numbear of model parameters and memory compared to existing algorithms.Maschinelles Lernen hat in den letzten Jahren bemerkenswerte Fortschritte in verschiedenen Forschungs- und Anwendungsbereichen ermöglicht. Das primäre Ziel des maschinellen Lernens besteht darin, Algorithmen zu entwickeln, die durch Beobachtung und Erfahrung lernen und sich verbessern können. Algorithmen des maschinellen Lernens lernen aus Daten, die verschiedene Formen von Komplexität aufweisen können, was grundlegende Herausforderungen mit sich bringt. Im Rahmen dieser Dissertation werden zwei Haupttypen von Datenkomplexität behandelt: Erstens weisen Daten oft inhärente Verbindungen, die durch einen einzelnen oder mehrere Graphen modelliert werden können. Methoden des maschinellen Lernens können diese Verbindungen potenziell ausnutzen, um beispielsweise Gruppen ähnlicher Nutzer in einem sozialen Netzwerk für gezieltes Marketing zu finden oder um funktionale Eigenschaften von Proteinen für das Design von Medikamenten vorherzusagen. Zweitens sind die Daten oft hochdimensional, z. B. aufgrund einer großen Anzahl von erfassten Merkmalen oder bedingt durch ein quadratisches Pixelraster auf Bildern. Klassische Methoden des maschinellen Lernens versagen immer wieder, wenn sie hochdimensionalen Daten ausgesetzt werden, da mehrere Schlüsselannahmen nicht mehr erfüllt sind. Daher besteht eine große Herausforderung beim maschinellen Lernen auf Graphen und hochdimensionalen Daten darin, sinnvolle Repräsentationen dieser Daten abzuleiten, die es den Modellen ermöglichen, effektiv zu lernen. Im Gegensatz zu konventionellen manuellen Feature-Engineering-Methoden zielt Representation Learning darauf ab, automatisch Datenrepräsentationen zu lernen, die für eine bestimmte Aufgabenstellung besonders geeignet sind. Angetrieben durch eine rasant steigende Datenverfügbarkeit haben diese Methoden bei Aufgaben wie der Objekterkennung in Bildern und der Spracherkennung enorme Erfolge gefeiert. Es besteht jedoch noch ein erheblicher Forschungsbedarf, um solche Verfahren für das Lernen auf Graphen und hochdimensionalen Daten voll auszuschöpfen. Diese Dissertation beschäftigt sich mit dem Problem des Lernens sinnvoller Repräsentationen für hocheffektives maschinelles Lernen auf komplexen Daten, insbesondere auf Graphen und hochdimensionalen Daten. Zusätzlich sind die meisten hier vorgeschlagenen Methoden hoch skalierbar, so dass sie aus großen Datenmengen lernen können. Obgleich eine breite Palette von allgemeinen Lernproblemen mit verschiedenen Arten der Überwachung adressiert wird, die von unüberwachten Problemen auf unannotierten Daten bis hin zum (semi-)überwachten Lernen auf annotierten Datensätzen reichen, werden die vorgestellten Metoden anhand spezifischen Anwendungen aus Bereichen wie der Analyse sozialer Netzwerke, der Informationssicherheit und der Computer Vision evaluiert. Der erste Teil der Dissertation befasst sich mit dem Representation Learning auf Graphen. Während existierende neuronale Netze für Graphen üblicherweise eine synchrone Nachrichtenübermittlung zwischen den Knoten durchführen und somit mit langreichweitigen Abhängigkeiten und Effizienzproblemen zu kämpfen haben, führt die erste hier vorgeschlagene Methode eine schnelle asynchrone Nachrichtenübermittlung durch und unterstützt somit adaptives und effizientes Lernen und skaliert zudem auf große Graphen. Ein weiterer Beitrag besteht in einem neuartigen graphenbasierten Ansatz zur Malware-Erkennung und -Klassifizierung auf Basis des Netzwerkverkehrs. Während bestehende Methoden einzelne Netzwerkflüsse zwischen zwei Endpunkten klassifizieren, sammelt der vorgeschlagene Algorithmus den gesamten Verkehr in einem überwachten Netzwerk innerhalb eines bestimmten Zeitraums und baut einen Kommunikationsgraphen auf, der dann mithilfe eines neuartigen neuronalen Netzes für Graphen klassifiziert wird. Das entwickelte Modell kann allgemein für weitere Graphenklassifizierungs- oder Anomalieerkennungsaufgaben eingesetzt werden. Zwei weitere Beiträge stellen eine gängige Annahme von Graphen-Lernmethoden in Frage, die so genannte Homophilie-Annahme, die besagt, dass Knoten mit ähnlichen Eigenschaften in der Regel eng im Graphen verbunden sind. Zu diesem Zweck wird eine Methode entwickelt, die Eigenschaften auf Knotenebene vorhersagt, indem sie die Verteilung der annotierten Klassen in der Nachbarschaft des jeweiligen Knotens nutzt. Das erlaubt dem vorgeschlagenen Modell, allgemeine Beziehungen zwischen einem Knoten und seinen Nachbarn zu lernen, die nicht auf Homophilie beschränkt sind. Eine weitere vorgeschlagene Methode modelliert strukturelle Ähnlichkeit zwischen Knoten, um unterschiedliche Rollen zu modellieren, zum Beispiel Influencer und Follower in einem sozialen Netzwerk. Insbesondere entwickeln wir einen unüberwachten Algorithmus zur Ableitung von Knoten-Deskriptoren, die darauf basieren, wie Knoten Wahrscheinlichkeitsmasse auf ihre Nachbarn verteilen, und aggregieren diese Deskriptoren, um ganze Graphen darzustellen. Der zweite Teil dieser Dissertation befasst sich mit dem Representation Learning auf hochdimensionalen Daten. Konkret wird das Problem des Clusterns hochdimensionaler Daten, wie z. B. Bilder, Texte oder Genexpressionsprofile, betrachtet. Klassische Clustering-Algorithmen haben mit dieser Art von Daten zu kämpfen, da in der Regel nicht davon ausgegangen werden kann, dass die Datenobjekte in Bezug auf alle Attribute ähnlich sind, sondern nur innerhalb eines bestimmten Unterraums des volldimensionalen Datenraums. Das Unterraum-Clustering ist ein Ansatz zum Clustern hochdimensionaler Daten, der auf dieser Annahme basiert. Obwohl es bereits leistungsfähige, auf neuronalen Netzen basierende Unterraum-Clustering-Methoden gibt, leiden diese Methoden im Allgemeinen unter Skalierbarkeitsproblemen und es fehlt ihnen an einer theoretischen Grundlage. Zu diesem Zweck wird ein neuartiger Metric Learning Ansatz für das Unterraum-Clustering vorgeschlagen, der unter geeigneten Annahmen nachweislich lineare Unterräume detektieren kann und gleichzeitig die erforderliche Anzahl von Modellparametern und Speicher im Vergleich zu bestehenden Algorithmen enorm reduziert

Efficient Machine Learning Approach for Optimizing Scientific Computing Applications on Emerging HPC Architectures

Efficient parallel implementations of scientific applications on multi-core CPUs with accelerators such as GPUs and Xeon Phis is challenging. This requires - exploiting the data parallel architecture of the accelerator along with the vector pipelines of modern x86 CPU architectures, load balancing, and efficient memory transfer between different devices. It is relatively easy to meet these requirements for highly-structured scientific applications. In contrast, a number of scientific and engineering applications are unstructured. Getting performance on accelerators for these applications is extremely challenging because many of these applications employ irregular algorithms which exhibit data-dependent control-flow and irregular memory accesses. Furthermore, these applications are often iterative with dependency between steps, and thus making it hard to parallelize across steps. As a result, parallelism in these applications is often limited to a single step. Numerical simulation of charged particles beam dynamics is one such application where the distribution of work and memory access pattern at each time step is irregular. Applications with these properties tend to present significant branch and memory divergence, load imbalance between different processor cores, and poor compute and memory utilization. Prior research on parallelizing such irregular applications have been focused around optimizing the irregular, data-dependent memory accesses and control-flow during a single step of the application independent of the other steps, with the assumption that these patterns are completely unpredictable. We observed that the structure of computation leading to control-flow divergence and irregular memory accesses in one step is similar to that in the next step. It is possible to predict this structure in the current step by observing the computation structure of previous steps. In this dissertation, we present novel machine learning based optimization techniques to address the parallel implementation challenges of such irregular applications on different HPC architectures. In particular, we use supervised learning to predict the computation structure and use it to address the control-flow and memory access irregularities in the parallel implementation of such applications on GPUs, Xeon Phis, and heterogeneous architectures composed of multi-core CPUs with GPUs or Xeon Phis. We use numerical simulation of charged particles beam dynamics simulation as a motivating example throughout the dissertation to present our new approach, though they should be equally applicable to a wide range of irregular applications. The machine learning approach presented here use predictive analytics and forecasting techniques to adaptively model and track the irregular memory access pattern at each time step of the simulation to anticipate the future memory access pattern. Access pattern forecasts can then be used to formulate optimization decisions during application execution which improves the performance of the application at a future time step based on the observations from earlier time steps. In heterogeneous architectures, forecasts can also be used to improve the memory performance and resource utilization of all the processing units to deliver a good aggregate performance. We used these optimization techniques and anticipation strategy to design a cache-aware, memory efficient parallel algorithm to address the irregularities in the parallel implementation of charged particles beam dynamics simulation on different HPC architectures. Experimental result using a diverse mix of HPC architectures shows that our approach in using anticipation strategy is effective in maximizing data reuse, ensuring workload balance, minimizing branch and memory divergence, and in improving resource utilization

Machine Learning

Machine Learning can be defined in various ways related to a scientific domain concerned with the design and development of theoretical and implementation tools that allow building systems with some Human Like intelligent behavior. Machine learning addresses more specifically the ability to improve automatically through experience

Joint optimization of manifold learning and sparse representations for face and gesture analysis

Face and gesture understanding algorithms are powerful enablers in intelligent vision systems for surveillance, security, entertainment, and smart spaces. In the future, complex networks of sensors and cameras may disperse directions to lost tourists, perform directory lookups in the office lobby, or contact the proper authorities in case of an emergency. To be effective, these systems will need to embrace human subtleties while interacting with people in their natural conditions. Computer vision and machine learning techniques have recently become adept at solving face and gesture tasks using posed datasets in controlled conditions. However, spontaneous human behavior under unconstrained conditions, or in the wild, is more complex and is subject to considerable variability from one person to the next. Uncontrolled conditions such as lighting, resolution, noise, occlusions, pose, and temporal variations complicate the matter further. This thesis advances the field of face and gesture analysis by introducing a new machine learning framework based upon dimensionality reduction and sparse representations that is shown to be robust in posed as well as natural conditions. Dimensionality reduction methods take complex objects, such as facial images, and attempt to learn lower dimensional representations embedded in the higher dimensional data. These alternate feature spaces are computationally more efficient and often more discriminative. The performance of various dimensionality reduction methods on geometric and appearance based facial attributes are studied leading to robust facial pose and expression recognition models. The parsimonious nature of sparse representations (SR) has successfully been exploited for the development of highly accurate classifiers for various applications. Despite the successes of SR techniques, large dictionaries and high dimensional data can make these classifiers computationally demanding. Further, sparse classifiers are subject to the adverse effects of a phenomenon known as coefficient contamination, where for example variations in pose may affect identity and expression recognition. This thesis analyzes the interaction between dimensionality reduction and sparse representations to present a unified sparse representation classification framework that addresses both issues of computational complexity and coefficient contamination. Semi-supervised dimensionality reduction is shown to mitigate the coefficient contamination problems associated with SR classifiers. The combination of semi-supervised dimensionality reduction with SR systems forms the cornerstone for a new face and gesture framework called Manifold based Sparse Representations (MSR). MSR is shown to deliver state-of-the-art facial understanding capabilities. To demonstrate the applicability of MSR to new domains, MSR is expanded to include temporal dynamics. The joint optimization of dimensionality reduction and SRs for classification purposes is a relatively new field. The combination of both concepts into a single objective function produce a relation that is neither convex, nor directly solvable. This thesis studies this problem to introduce a new jointly optimized framework. This framework, termed LGE-KSVD, utilizes variants of Linear extension of Graph Embedding (LGE) along with modified K-SVD dictionary learning to jointly learn the dimensionality reduction matrix, sparse representation dictionary, sparse coefficients, and sparsity-based classifier. By injecting LGE concepts directly into the K-SVD learning procedure, this research removes the support constraints K-SVD imparts on dictionary element discovery. Results are shown for facial recognition, facial expression recognition, human activity analysis, and with the addition of a concept called active difference signatures, delivers robust gesture recognition from Kinect or similar depth cameras