The "MIND" Scalable PIM Architecture

MIND (Memory, Intelligence, and Network Device) is an advanced parallel computer architecture for high performance computing and scalable embedded processing. It is a Processor-in-Memory (PIM) architecture integrating both DRAM bit cells and CMOS logic devices on the same silicon die. MIND is multicore with multiple memory/processor nodes on each chip and supports global shared memory across systems of MIND components. MIND is distinguished from other PIM architectures in that it incorporates mechanisms for efficient support of a global parallel execution model based on the semantics of message-driven multithreaded split-transaction processing. MIND is designed to operate either in conjunction with other conventional microprocessors or in standalone arrays of like devices. It also incorporates mechanisms for fault tolerance, real time execution, and active power management. This paper describes the major elements and operational methods of the MIND architecture

Trace-level speculative multithreaded architecture

This paper presents a novel microarchitecture to exploit trace-level speculation by means of two threads working cooperatively in a speculative and non-speculative way respectively. The architecture presents two main benefits: (a) no significant penalties are introduced in the presence of a misspeculation and (b) any type of trace predictor can work together with this proposal. In this way, aggressive trace predictors can be incorporated since misspeculations do not introduce significant penalties. We describe in detail TSMA (trace-level speculative multithreaded architecture) and present initial results to show the benefits of this proposal. We show how simple trace predictors achieve significant speed-up in the majority of cases. Results of a simple trace speculation mechanism show an average speed-up of 16%.Peer ReviewedPostprint (published version

Improving latency tolerance of multithreading through decoupling

The increasing hardware complexity of dynamically scheduled superscalar processors may compromise the scalability of this organization to make an efficient use of future increases in transistor budget. SMT processors, designed over a superscalar core, are therefore directly concerned by this problem. The article presents and evaluates a novel processor microarchitecture which combines two paradigms: simultaneous multithreading and access/execute decoupling. Since its decoupled units issue instructions in order, this architecture is significantly less complex, in terms of critical path delays, than a centralized out-of-order design, and it is more effective for future growth in issue-width and clock speed. We investigate how both techniques complement each other. Since decoupling features an excellent memory latency hiding efficiency, the large amount of parallelism exploited by multithreading may be used to hide the latency of functional units and keep them fully utilized. The study shows that, by adding decoupling to a multithreaded architecture, fewer threads are needed to achieve maximum throughput. Therefore, in addition to the obvious hardware complexity reduction, it places lower demands on the memory system. The study also reveals that multithreading by itself exhibits little memory latency tolerance. Results suggest that most of the latency hiding effectiveness of SMT architectures comes from the dynamic scheduling. On the other hand, decoupling is very effective at hiding memory latency. An increase in the cache miss penalty from 1 to 32 cycles reduces the performance of a 4-context multithreaded decoupled processor by less than 2 percent. For the nondecoupled multithreaded processor, the loss of performance is about 23 percent.Peer ReviewedPostprint (published version

NCESPARC+: an implementation of a SPARC architecture with hardware support to multithreading for the multiplus multiprocessor

NCESP ARC + is an implementation of the SP ARC v: 8 architecture with hardware support to a variable number of thread contexts, which is under development for use within the framework of the Multiplus distributed shared-memory multiprocessor. It is expected to provide an efficient and automatic mechanism to hide the latency of busy-waiting synchronization loops, cachecoherence protocol and remote memory access operations within the Multiplus multiprocessor. NCESPARC + performs context-switching in at most four processor cycles whenever there is an instruction cache miss, a data dependency in relation to the destination operand of a pending load instruction or a busy-waiting synchronization loop. It has a decoupled architecture which allows the main pipeline to process instructions from a given context while the Memory Interface Unit performs memory access operations related to that same context or to any other context. Results of simulation experiments show the impact of some architectural parameters on the NCESPARC + processor performance and demonstrate that the use of multiple thread contexts can e.ffectively produce a much better utilization of the processor when long latency operations are performed In addition, NCESPARC + processor performance with a single context is superior to that of a standard implementation of the SPARC architecture due to its decoupled architecture

MGSim - Simulation tools for multi-core processor architectures

MGSim is an open source discrete event simulator for on-chip hardware components, developed at the University of Amsterdam. It is intended to be a research and teaching vehicle to study the fine-grained hardware/software interactions on many-core and hardware multithreaded processors. It includes support for core models with different instruction sets, a configurable multi-core interconnect, multiple configurable cache and memory models, a dedicated I/O subsystem, and comprehensive monitoring and interaction facilities. The default model configuration shipped with MGSim implements Microgrids, a many-core architecture with hardware concurrency management. MGSim is furthermore written mostly in C++ and uses object classes to represent chip components. It is optimized for architecture models that can be described as process networks.Comment: 33 pages, 22 figures, 4 listings, 2 table

Out-of-Order Retirement of Instructions in Superscalar, Multithreaded, and Multicore Processors

Los procesadores superescalares actuales utilizan un reorder buffer (ROB) para contabilizar las instrucciones en vuelo. El ROB se implementa como una cola FIFO first in first out en la que las instrucciones se insertan en orden de programa después de ser decodificadas, y de la que se extraen también en orden de programa en la etapa commit. El uso de esta estructura proporciona un soporte simple para la especulación, las excepciones precisas y la reclamación de registros. Sin embargo, el hecho de retirar instrucciones en orden puede degradar las prestaciones si una operación de alta latencia está bloqueando la cabecera del ROB. Varias propuestas se han publicado atacando este problema. La mayoría utiliza retirada de instrucciones fuera de orden de forma especulativa, requiriendo almacenar puntos de recuperación (checkpoints) para restaurar un estado válido del procesador ante un fallo de especulación. Normalmente, los checkpoints necesitan implementarse con estructuras hardware costosas, y además requieren un crecimiento de otras estructuras del procesador, lo cual a su vez puede impactar en el tiempo de ciclo de reloj. Este problema afecta a muchos tipos de procesadores actuales, independientemente del número de hilos hardware (threads) y del número de núcleos de cómputo (cores) que incluyan. Esta tesis abarca el estudio de la retirada no especulativa de instrucciones fuera de orden en procesadores superescalares, multithread y multicore.Ubal Tena, R. (2010). Out-of-Order Retirement of Instructions in Superscalar, Multithreaded, and Multicore Processors [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8535Palanci

Investigation of a simultaneous multithreaded architecture

Many enhancements have been made to the traditional general purpose load-store computer architectures. Among the enhancements are memory hierarchy improvements, branch prediction, and multiple issue processors. A major problem that exists with current microprocessor design is the disparity in the much larger increase in speed of the CPU versus the moderate increase in speed accessing main memory. The simultaneous multithreaded architecture is an extension of the single-threaded architecture that helps hide the performance penalty created by long-latency instructions, branch mispredictions, and memory accesses. Simultaneous multithreaded architectures use a more flexible parallelism, which takes advantage of both instruction-level, and thread-level parallelism. The goal of this project was to design, simulate, and analyze a model of a simultaneous multithreaded architecture in order to evaluate design alternatives. The simulator was created by modifying a version of the Simple Scalar toolset, developed at the University of Wisconsin. The simulations provide documentation for an overall system performance improvement of a simulta neous multithreaded architecture. In early simulation results, performed with the same number of functional units, an improvement in the number of instructions per cycle (IPC) of between 43% and 58% was found using four threads versus a single thread. The horizontal waste rate, which measures the number of unused issue slots, was reduced between 35% and 46%. The vertical waste rate, which measures the percentage- of unused issue cycles (no issue slots used in a cycle), was reduced between 46% and 61%. These results are derived from a set of four sample programs. It was also found that increasing the number of certain functional units did not improve performance, whereas increasing the number of other types of functional units did have a significant positive impact on performance