Rapid Prototyping and Exploration Environment for Generating C-to-Hardware-Compilers

There is today an ever-increasing demand for more computational power coupled with a desire to minimize energy requirements. Hardware accelerators currently appear to be the best solution to this problem. While general purpose computation with GPUs seem to be very successful in this area, they perform adequately only in those cases where the data access patterns and utilized algorithms fit the underlying architecture. ASICs on the other hand can yield even better results in terms of performance and energy consumption, but are very inflexible, as they are manufactured with an application specific circuitry. Field Programmable Gate Arrays (FPGAs) represent a combination of approaches: With their application specific hardware they provide high computational power while requiring, for many applications, less energy than a CPU or a GPU. On the other hand they are far more flexible than an ASIC due to their reconfigurability. The only remaining problem is the programming of the FPGAs, as they are far more difficult to program compared to regular software. To allow common software developers, who have at best very limited knowledge in hardware design, to make use of these devices, tools were developed that take a regular high level language and generate hardware from it. Among such tools, C-to-HDL compilers are a particularly wide-spread approach. These compilers attempt to translate common C code into a hardware description language from which a datapath is generated. Most of these compilers have many restrictions for the input and differ in their underlying generated micro architecture, their scheduling method, their applied optimizations, their execution model and even their target hardware. Thus, a comparison of a certain aspect alone, like their implemented scheduling method or their generated micro architecture, is almost impossible, as they differ in so many other aspects. This work provides a survey of the existing C-to-HDL compilers and presents a new approach to evaluating and exploring different micro architectures for dynamic scheduling used by such compilers. From a mathematically formulated rule set the Triad compiler generates a backend for the Scale compiler framework, which then implements a hardware generation backend with described dynamic scheduling. While more than a factor of four slower than hardware from highly optimized compilers, this environment allows easy comparison and exploration of different rule sets and the micro architecture for the dynamically scheduled datapaths generated from them. For demonstration purposes a rule set modeling the COCOMA token flow model from the COMRADE 2.0 compiler was implemented. Multiple variants of it were explored: Savings of up to 11% of the required hardware resources were possible

A model-based approach for the specification and refinement of streaming applications

Embedded systems can be found in a wide range of applications. Depending on the application, embedded systems must meet a wide range of constraints. Thus, designing and programming embedded systems is a challenging task. Here, model-based design flows can be a solution. This thesis proposes novel approaches for the specification and refinement of streaming applications. To this end, it focuses on dataflow models. As key result, the proposed dataflow model provides for a seamless model-based design flow from system level to the instruction/logic level for a wide range of streaming applications

실시간 임베디드 시스템을 위한 동적 행위 명세 및 설계 공간 탐색 기법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2016. 8. 하순회.하나의 칩에 집적되는 프로세서의 개수가 많아지고, 많은 기능들이 통합됨에 따라, 연산양의 변화, 서비스의 품질, 예상치 못한 시스템 요소의 고장 등과 같은 다양한 요소들에 의해 시스템의 상태가 동적으로 변화하게 된다. 반면에, 본 논문에서 주된 관심사를 가지는 스마트 폰 장치에서 주로 사용되는 비디오, 그래픽 응용들의 경우, 계산 복잡도가 지속적으로 증가하고 있다. 따라서, 이렇게 동적으로 변하는 행위를 가지면서도 병렬성을 내제한 계산 집약적인 연산을 포함하는 복잡한 시스템을 구현하기 위해서는 체계적인 설계 방법론이 고도로 요구된다. 모델 기반 방법론은 병렬 임베디드 소프트웨어 개발을 위한 대표적인 방법 중 하나이다. 특히, 시스템 명세, 정적 성능 분석, 설계 공간 탐색, 그리고 자동 코드 생성까지의 모든 설계 단계를 지원하는 병렬 임베디드 소프트웨어 설계 환경으로서, HOPES 프레임워크가 제시되었다. 다른 설계 환경들과는 다르게, 이기종 멀티프로세서 아키텍처에서의 일반적인 수행 모델로서, 공통 중간 코드 (CIC) 라고 부르는 프로그래밍 플랫폼이라는 새로운 개념을 소개하였다. CIC 태스크 모델은 프로세스 네트워크 모델에 기반하고 있지만, SDF 모델로 구체화될 수 있기 때문에, 병렬 처리뿐만 아니라 정적 분석이 용이하다는 장점을 가진다. 하지만, SDF 모델은 응용의 동적인 행위를 명세할 수 없다는 표현상의 제약을 가진다. 이러한 제약을 극복하고, 시스템의 동적 행위를 응용 외부와 내부로 구분하여 명세하기 위해, 본 논문에서는 데이터 플로우와 유한상태기 (FSM) 모델에 기반하여 확장된 CIC 태스크 모델을 제안한다. 상위 수준에서는, 각 응용은 데이터 플로우 태스크로 명세 되며, 동적 행위는 응용들의 수행을 감독하는 제어 태스크로 모델 된다. 데이터 플로우 태스크 내부는, 유한상태기 기반의 SADF 모델과 유사한 형태로 동적 행위가 명세 된다SDF 태스크는 복수개의 행위를 가질 수 있으며, 모드 전환기 (MTM)이라고 불리는 유한 상태기의 테이블 형태의 명세를 통해 SDF 그래프의 모드 전환 규칙을 명세 한다. 이를 MTM-SDF 그래프라고 부르며, 복수 모드 데이터 플로우 모델 중 하나라 구분된다. 응용은 유한한 행위 (또는 모드)를 가지며, 각 행위 (모드)는 SDF 그래프로 표현되는 것을 가정한다. 이를 통해 다양한 프로세서 개수에 대해 단위시간당 처리량을 최대화하는 컴파일-시간 스케줄링을 수행하고, 스케줄 결과를 저장할 수 있도록 한다. 또한, 복수 모드 데이터 플로우 그래프를 위한 멀티프로세서 스케줄링 기법을 제시한다. 복수 모드 데이터 플로우 그래프를 위한 몇몇 스케줄링 기법들이 존재하지만, 모드 사이에 태스크 이주를 허용한 기법들은 존재하지 않는다. 하지만 태스크 이주를 허용하게 되면 자원 요구량을 줄일 수 있다는 발견을 통해, 본 논문에서는 모드 사이의 태스크 이주를 허용하는 복수 모드 데이터 플로우 그래프를 위한 멀티프로세서 스케줄링 기법을 제안한다. 유전 알고리즘에 기반하여, 제안하는 기법은 자원 요구량을 최소화하기 위해 각 모드에 해당하는 모든 SDF 그래프를 동시에 스케줄 한다. 주어진 단위 시간당 처리량 제약을 만족시키기 위해, 제안하는 기법은 각 모드 별로 실제 처리량 요구량을 계산하며, 처리량의 불규칙성을 완화하기 위한 출력 버퍼의 크기를 계산한다. 명세된 태스크 그래프와 스케줄 결과로부터, HOPES 프레임워크는 대상 아키텍처를 위한 자동 코드 생성을 지원한다. 이를 위해 자동 코드 생성기는 CIC 태스크 모델의 확장된 특징들을 지원하도록 확장되었다. 응용 수준에서는 MTM-SDF 그래프를 주어진 정적 스케줄링 결과를 따르는 멀티프로세서 코드를 생성하도록 확장되었다. 또한, 네 가지 서로 다른 스케줄링 정책 (fully-static, self-timed, static-assignment, fully-dynamic)에 대한 멀티프로세서 코드 생성을 지원한다. 시스템 수준에서는 지원하는 시스템 요청 API에 대한 실제 구현 코드를 생성하며, 정적 스케줄 결과와 태스크들의 제어 가능한 속성들에 대한 자료 구조 코드를 생성한다. 복수 모드 멀티미디어 터미널 예제를 통한 기초적인 실험들을 통해, 제안하는 방법론의 타당성을 보인다.As the number of processors in a chip increases, and more functions are integrated, the system status will change dynamically due to various factors such as the workload variation, QoS requirement, and unexpected component failure. On the other hand, computation-complexity of user applications is also steadily increasingvideo and graphics applications are two major driving forces in smart mobile devices, which define the main application domain of interest in this dissertation. So, a systematic design methodology is highly required to implement such complex systems which contain dynamically changed behavior as well as computation-intensive workload that can be parallelized. A model-based approach is one of representative approaches for parallel embedded software development. Especially, HOPES framework is proposed which is a design environment for parallel embedded software supporting the overall design steps: system specification, performance estimation, design space exploration, and automatic code generation. Distinguished from other design environments, it introduces a novel concept of programming platform, called CIC (Common Intermediate Code) that can be understood as a generic execution model of heterogeneous multiprocessor architecture. The CIC task model is based on a process network model, but it can be refined to the SDF (Synchronous Data Flow) model, since it has a very desirable features for static analyzability as well as parallel processing. However, the SDF model has a typical weakness of expression capability, especially for the system-level specification and dynamically changed behavior of an application. To overcome this weakness, in this dissertation, we propose an extended CIC task model based on dataflow and FSM models to specify the dynamic behavior of the system distinguishing inter- and intra-application dynamism. At the top-level, each application is specified by a dataflow task and the dynamic behavior is modeled as a control task that supervises the execution of applications. Inside a dataflow task, it specifies the dynamic behavior using a similar way as FSM-based SADFan SDF task may have multiple behaviors and a tabular specification of an FSM, called MTM (Mode Transition Machine), describes the mode transition rules for the SDF graph. We call it to MTM-SDF model which is classified as multi-mode dataflow models in the dissertation. It assumes that an application has a finite number of behaviors (or modes) and each behavior (mode) is represented by an SDF graph. It enables us to perform compile-time scheduling of each graph to maximize the throughput varying the number of allocated processors, and store the scheduling information. Also, a multiprocessor scheduling technique is proposed for a multi-mode dataflow graph. While there exist several scheduling techniques for multi-mode dataflow models, no one allows task migration between modes. By observing that the resource requirement can be additionally reduced if task migration is allowed, we propose a multiprocessor scheduling technique of a multi-mode dataflow graph considering task migration between modes. Based on a genetic algorithm, the proposed technique schedules all SDF graphs in all modes simultaneously to minimize the resource requirement. To satisfy the throughput constraint, the proposed technique calculates the actual throughput requirement of each mode and the output buffer size for tolerating throughput jitter. For the specified task graph and scheduling results, the CIC translator generates parallelized code for the target architecture. Therefore the CIC translator is extended to support extended features of the CIC task model. In application-level, it is extended to support multiprocessor code generation for an MTM-SDF graph considering the given static scheduling results. Also, multiprocessor code generation of four different scheduling policies are supported for an MTM-SDF graph: fully-static, self-timed, static-assignment, and fully-dynamic. In system-level, the CIC translator is extended to support code generation for implementation of system request APIs and data structures for the static scheduling results and configurable task parameters. Through preliminary experiments with a multi-mode multimedia terminal example, the viability of the proposed methodology is verified.Chapter 1 Introduction 1 1.1 Motivation 1 1.2 Contribution 7 1.3 Dissertation organization 9 Chapter 2 Background 10 2.1 Related work 10 2.1.1 Compiler-based approach 10 2.1.2 Language-based approach 11 2.1.3 Model-based approach 15 2.2 HOPES framework 19 2.3 Common Intermediate Code (CIC) Model 21 Chapter 3 Dynamic Behavior Specification 26 3.1 Problem definition 26 3.1.1 System-level dynamic behavior 26 3.1.2 Application-level dynamic behavior 27 3.2 Related work 28 3.3 Motivational example 31 3.4 Control task specification for system-level dynamism 33 3.4.1 Internal specification 33 3.4.2 Action scripts 38 3.5 MTM-SDF specification for application-level dynamism 44 3.5.1 MTM specification 44 3.5.2 Task graph specification 45 3.5.3 Execution semantic of an MTM-SDF graph 46 Chapter 4 Multiprocessor Scheduling of an Multi-mode Dataflow Graph 50 4.1 Related work 51 4.2 Motivational example 56 4.2.1 Throughput requirement calculation considering mode transition delay 56 4.2.2 Task migration between mode transition 58 4.3 Problem definition 61 4.4 Throughput requirement analysis 65 4.4.1 Mode transition delay 66 4.4.2 Arrival curves of the output buffer 70 4.4.3 Buffer size determination 71 4.4.4 Throughput requirement analysis 73 4.5 Proposed MMDF scheduling framework 75 4.5.1 Optimization problem 75 4.5.2 GA configuration 76 4.5.3 Fitness function 78 4.5.4 Local optimization technique 79 4.6 Experimental results 81 4.6.1 MMDF scheduling technique 83 4.6.2 Scalability of the Proposed Framework 88 Chapter 5 Multiprocessor Code Generation for the Extended CIC Model 89 5.1 CIC translator 89 5.2 Code generation for application-level dynamism 91 5.2.1 Function call-style code generation (fully-static, self-timed) 94 5.2.2 Thread-style code generation (static-assignment, fully-dynamic) 98 5.3 Code generation for system-level dynamism 101 5.4 Experimental results 105 Chapter 6 Conclusion and Future Work 107 Bibliography 109 초록 125Docto

A hardware-software codesign framework for cellular computing

Until recently, the ever-increasing demand of computing power has been met on one hand by increasing the operating frequency of processors and on the other hand by designing architectures capable of exploiting parallelism at the instruction level through hardware mechanisms such as super-scalar execution. However, both these approaches seem to have reached a plateau, mainly due to issues related to design complexity and cost-effectiveness. To face the stabilization of performance of single-threaded processors, the current trend in processor design seems to favor a switch to coarser-grain parallelization, typically at the thread level. In other words, high computational power is achieved not only by a single, very fast and very complex processor, but through the parallel operation of several processors, each executing a different thread. Extrapolating this trend to take into account the vast amount of on-chip hardware resources that will be available in the next few decades (either through further shrinkage of silicon fabrication processes or by the introduction of molecular-scale devices), together with the predicted features of such devices (e.g., the impossibility of global synchronization or higher failure rates), it seems reasonable to foretell that current design techniques will not be able to cope with the requirements of next-generation electronic devices and that novel design tools and programming methods will have to be devised. A tempting source of inspiration to solve the problems implied by a massively parallel organization and inherently error-prone substrates is biology. In fact, living beings possess characteristics, such as robustness to damage and self-organization, which were shown in previous research as interesting to be implemented in hardware. For instance, it was possible to realize relatively simple systems, such as a self-repairing watch. Overall, these bio-inspired approaches seem very promising but their interest for a wider audience is problematic because their heavily hardware-oriented designs lack some of the flexibility achievable with a general purpose processor. In the context of this thesis, we will introduce a processor-grade processing element at the heart of a bio-inspired hardware system. This processor, based on a single-instruction, features some key properties that allow it to maintain the versatility required by the implementation of bio-inspired mechanisms and to realize general computation. We will also demonstrate that the flexibility of such a processor enables it to be evolved so it can be tailored to different types of applications. In the second half of this thesis, we will analyze how the implementation of a large number of these processors can be used on a hardware platform to explore various bio-inspired mechanisms. Based on an extensible platform of many FPGAs, configured as a networked structure of processors, the hardware part of this computing framework is backed by an open library of software components that provides primitives for efficient inter-processor communication and distributed computation. We will show that this dual software–hardware approach allows a very quick exploration of different ways to solve computational problems using bio-inspired techniques. In addition, we also show that the flexibility of our approach allows it to exploit replication as a solution to issues that concern standard embedded applications

An automated OpenCL FPGA compilation framework targeting a configurable, VLIW chip multiprocessor

Modern system-on-chips augment their baseline CPU with coprocessors and accelerators to increase overall computational capacity and power efficiency, and thus have evolved into heterogeneous systems. Several languages have been developed to enable this paradigm shift, including CUDA and OpenCL. This thesis discusses a unified compilation environment to enable heterogeneous system design through the use of OpenCL and a customised VLIW chip multiprocessor (CMP) architecture, known as the LE1. An LLVM compilation framework was researched and a prototype developed to enable the execution of OpenCL applications on the LE1 CPU. The framework fully automates the compilation flow and supports work-item coalescing to better utilise the CPU cores and alleviate the effects of thread divergence. This thesis discusses in detail both the software stack and target hardware architecture and evaluates the scalability of the proposed framework on a highly precise cycle-accurate simulator. This is achieved through the execution of 12 benchmarks across 240 different machine configurations, as well as further results utilising an incomplete development branch of the compiler. It is shown that the problems generally scale well with the LE1 architecture, up to eight cores, when the memory system becomes a serious bottleneck. Results demonstrate superlinear performance on certain benchmarks (x9 for the bitonic sort benchmark with 8 dual-issue cores) with further improvements from compiler optimisations (x14 for bitonic with the same configuration

Cost-Efficient Soft-Error Resiliency for ASIP-based Embedded Systems

Recent decades have witnessed the rapid growth of embedded systems. At present, embedded systems are widely applied in a broad range of critical applications including automotive electronics, telecommunication, healthcare, industrial electronics, consumer electronics military and aerospace. Human society will continue to be greatly transformed by the pervasive deployment of embedded systems. Consequently, substantial amount of efforts from both industry and academic communities have contributed to the research and development of embedded systems. Application-specific instruction-set processor (ASIP) is one of the key advances in embedded processor technology, and a crucial component in some embedded systems. Soft errors have been directly observed since the 1970s. As devices scale, the exponential increase in the integration of computing systems occurs, which leads to correspondingly decrease in the reliability of computing systems. Today, major research forums state that soft errors are one of the major design technology challenges at and beyond the 22 nm technology node. Therefore, a large number of soft-error solutions, including error detection and recovery, have been proposed from differing perspectives. Nonetheless, most of the existing solutions are designed for general or high-performance systems which are different to embedded systems. For embedded systems, the soft-error solutions must be cost-efficient, which requires the tailoring of the processor architecture with respect to the feature of the target application. This thesis embodies a series of explorations for cost-efficient soft-error solutions for ASIP-based embedded systems. In this exploration, five major solutions are proposed. The first proposed solution realizes checkpoint recovery in ASIPs. By generating customized instructions, ASIP-implemented checkpoint recovery can perform at a finer granularity than what was previously possible. The fault-free performance overhead of this solution is only 1.45% on average. The recovery delay is only 62 cycles at the worst case. The area and leakage power overheads are 44.4% and 45.6% on average. The second solution explores utilizing two primitive error recovery techniques jointly. This solution includes three application-specific optimization methodologies. This solution generates the optimized error-resilient ASIPs, based on the characteristics of primitive error recovery techniques, static reliability analysis and design constraints. The resultant ASIP can be configured to perform at runtime according to the optimized recovery scheme. This solution can strategically enhance cost-efficiency for error recovery. In order to guarantee cost-efficiency in unpredictable runtime situations, the third solution explores runtime adaptation for error recovery. This solution aims to budget and adapt the error recovery operations, so as to spend the resources intelligently and to tolerate adverse influences of runtime variations. The resultant ASIP can make runtime decisions to determine the activation of spatial and temporal redundancies, according to the runtime situations. At the best case, this solution can achieve almost 50x reliability gain over the state of the art solutions. Given the increasing demand for multi-core computing systems, the last two proposed solutions target error recovery in multi-core ASIPs. The first solution of these two explores ASIP-implemented fine-grained process migration. This solution is a key infrastructure, which allows cost-efficient task management, for realizing cost-efficient soft-error recovery in multi-core ASIPs. The average time cost is only 289 machine cycles to perform process migration. The last solution explores using dynamic and adaptive mapping to assign heterogeneous recovery operations to the tasks in the multi-core context. This solution allows each individual ASIP-based processing core to dynamically adapt its specific error recovery functionality according to the corresponding task's characteristics, in terms of soft error vulnerability and execution time deadline. This solution can significantly improve the reliability of the system by almost two times, with graceful constraint penalty, in comparison to the state-of-the-art counterparts