Reducing cache coherence traffic with a NUMA-aware runtime approach

Cache Coherent NUMA (ccNUMA) architectures are a widespread paradigm due to the benefits they provide for scaling core count and memory capacity. Also, the flat memory address space they offer considerably improves programmability. However, ccNUMA architectures require sophisticated and expensive cache coherence protocols to enforce correctness during parallel executions, which trigger a significant amount of on- and off-chip traffic in the system. This paper analyses how coherence traffic may be best constrained in a large, real ccNUMA platform comprising 288 cores through the use of a joint hardware/software approach. For several benchmarks, we study coherence traffic in detail under the influence of an added hierarchical cache layer in the directory protocol combined with runtime managed NUMA-aware scheduling and data allocation techniques to make most efficient use of the added hardware. The effectiveness of this joint approach is demonstrated by speedups of 3.14× to 9.97× and coherence traffic reductions of up to 99% in comparison to NUMA-oblivious scheduling and data allocation.This work has been supported by the Spanish Government (Severo Ochoa grants SEV2015-0493), by the Spanish Ministry of Science and Innovation (contracts TIN2015-65316-P), by the Generalitat de Catalunya (contracts 2014-SGR-1051 and 2014-SGR-1272), by the RoMoL ERC Advanced Grant (GA 321253) and the European HiPEAC Network of Excellence. The Mont-Blanc project receives funding from the EU’s H2020 Framework Programme (H2020/2014-2020) under grant agreement no 671697. M. Moretó has been partially supported by the Ministry of Economy and Competitiveness under Juan de la Cierva postdoctoral fellowship number JCI-2012-15047. M. Casas is supported by the Secretary for Universities and Research of the Ministry of Economy and Knowledge of the Government of Catalonia and the Cofund programme of the Marie Curie Actions of the 7th R&D Framework Programme of the European Union (Contract 2013 BP B 00243).Peer ReviewedPostprint (author's final draft

Path-Based partitioning methods for 3D Networks-on-Chip with minimal adaptive routing

© 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Combining the benefits of 3D ICs and Networks-on-Chip (NoCs) schemes provides a significant performance gain in Chip Multiprocessors (CMPs) architectures. As multicast communication is commonly used in cache coherence protocols for CMPs and in various parallel applications, the performance of these systems can be significantly improved if multicast operations are supported at the hardware level. In this paper, we present several partitioning methods for the path-based multicast approach in 3D mesh-based NoCs, each with different levels of efficiency. In addition, we develop novel analytical models for unicast and multicast traffic to explore the efficiency of each approach. In order to distribute the unicast and multicast traffic more efficiently over the network, we propose the Minimal and Adaptive Routing (MAR) algorithm for the presented partitioning methods. The analytical and experimental results show that an advantageous method named Recursive Partitioning (RP) outperforms the other approaches. RP recursively partitions the network until all partitions contain a comparable number of switches and thus the multicast traffic is equally distributed among several subsets and the network latency is considerably decreased. The simulation results reveal that the RP method can achieve performance improvement across all workloads while performance can be further improved by utilizing the MAR algorithm. Nineteen percent average and 42 percent maximum latency reduction are obtained on SPLASH-2 and PARSEC benchmarks running on a 64-core CMP.Ebrahimi, M.; Daneshtalab, M.; Liljeberg, P.; Plosila, J.; Flich Cardo, J.; Tenhunen, H. (2014). Path-Based partitioning methods for 3D Networks-on-Chip with minimal adaptive routing. IEEE Transactions on Computers. 63(3):718-733. doi:10.1109/TC.2012.255S71873363

Hardware thread scheduling algorithms for single-ISA asymmetric CMPs

Through the past several decades, based on the Moore's law, the semiconductor industry was doubling the number of transistors on the single chip roughly every eighteen months. For a long time this continuous increase in transistor budget drove the increase in performance as the processors continued to exploit the instruction level parallelism (ILP) of the sequential programs. This pattern hit the wall in the early years of the twentieth century when designing larger and more complex cores became difficult because of the power and complexity reasons. Computer architects responded by integrating many cores on the same die thereby creating Chip Multicore Processors (CMP). In the last decade, the computing technology experienced tremendous developments, Chip Multiprocessors (CMP) expanded from the symmetric and homogeneous to the asymmetric or heterogeneous Multiprocessors. Having cores of different types in a single processor enables optimizing performance, power and energy efficiency for a wider range of workloads. It enables chip designers to employ specialization (that is, we can use each type of core for the type of computation where it delivers the best performance/energy trade-off). The benefits of Asymmetric Chip Multiprocessors (ACMP) are intuitive as it is well known that different workloads have different resource requirements. The CMPs improve the performance of applications by exploiting the Thread Level Parallelism (TLP). Parallel applications relying on multiple threads must be efficiently managed and dispatched for execution if the parallelism is to be properly exploited. Since more and more applications become multi-threaded we expect to find a growing number of threads executing on a machine. Consequently, the operating system will require increasingly larger amounts of CPU time to schedule these threads efficiently. Thus, dynamic thread scheduling techniques are of paramount importance in ACMP designs since they can make or break performance benefits derived from the asymmetric hardware or parallel software. Several thread scheduling methods have been proposed and applied to ACMPs. In this thesis, we first study the state of the art thread scheduling techniques and identify the main reasons limiting the thread level parallelism in an ACMP systems. We propose three novel approaches to schedule and manage threads and exploit thread level parallelism implemented in hardware, instead of perpetuating the trend of performing more complex thread scheduling in the operating system. Our first goal is to improve the performance of an ACMP systems by improving thread scheduling at the hardware level. We also show that the hardware thread scheduling reduces the energy consumption of an ACMP systems by allowing better utilization of the underlying hardware.A través de las últimas décadas, con base en la ley de Moore, la industria de semiconductores duplica el número de transistores en el chip alrededor de una vez cada dieciocho meses. Durante mucho tiempo, este aumento continuo en el número de transistores impulsó el aumento en el rendimiento de los procesadores solo explotando el paralelismo a nivel de instrucción (ILP) y el aumento de la frecuencia de los procesadores, permitiendo un aumento del rendimiento de los programas secuenciales. Este patrón llego a su limite en los primeros años del siglo XX, cuando el diseño de procesadores más grandes y complejos se convirtió en una tareá difícil debido a las debido al consumo requerido. La respuesta a este problema por parte de los arquitectos fue la integración de muchos núcleos en el mismo chip creando así chip multinúcleo Procesadores (CMP). En la última década, la tecnología de la computación experimentado enormes avances, sobre todo el en chip multiprocesadores (CMP) donde se ha pasado de diseños simetricos y homogeneous a sistemas asimétricos y heterogeneous. Tener núcleos de diferentes tipos en un solo procesador permite optimizar el rendimiento, la potencia y la eficiencia energética para una amplia gama de cargas de trabajo. Permite a los diseñadores de chips emplear especialización (es decir, podemos utilizar un tipo de núcleo diferente para distintos tipos de cálculo dependiendo del trade-off respecto del consumo y rendimiento). Los beneficios de la asimétrica chip multiprocesadores (ACMP) son intuitivos, ya que es bien sabido que diferentes cargas de trabajo tienen diferentes necesidades de recursos. Los CMP mejoran el rendimiento de las aplicaciones mediante la explotación del paralelismo a nivel de hilo (TLP). En las aplicaciones paralelas que dependen de múltiples hilos, estos deben ser manejados y enviados para su ejecución, y el paralelismo se debe explotar de manera eficiente. Cada día hay mas aplicaciones multi-hilo, por lo tanto encotraremos un numero mayor de hilos que se estaran ejecutando en la máquina. En consecuencia, el sistema operativo requerirá cantidades cada vez mayores de tiempo de CPU para organizar y ejecutar estos hilos de manera eficiente. Por lo tanto, las técnicas de optimizacion dinámica para la organizacion de la ejecucion de hilos son de suma importancia en los diseños ACMP ya que pueden incrementar o dsiminuir el rendimiento del hardware asimétrico o del software paralelo. Se han propuesto y aplicado a ACMPs varios métodos de organizar y ejecutar los hilos. En esta tesis, primero estudiamos el estado del arte en las técnicas para la gestionar la ejecucion de los hilos y hemos identificado las principales razones que limitan el paralelismo en sistemas ACMP. Proponemos tres nuevos enfoques para programar y gestionar los hilos y explotar el paralelismo a nivel de hardware, en lugar de perpetuar la tendencia actual de dejar esta gestion cada vez maas compleja al sistema operativo. Nuestro primer objetivo es mejorar el rendimiento de un sistema ACMP mediante la mejora en la gestion de los hilos a nivel de hardware. También mostramos que la gestion del los hilos a nivel de hardware reduce el consumo de energía de un sistemas de ACMP al permitir una mejor utilización del hardware subyacente