A DVFS Cycle Accurate Simulation Framework with Asynchronous NoC Design for Power-Performance Optimizations

Network-on-Chip (NoC) is a flexible and scalable solution to interconnect multi-cores, with a strong influence on the performance of the whole chip. On-chip network affects also the overall power consumption, thus requiring accurate early-stage estimation and optimization methodologies. In this scenario, the Dynamic Voltage Frequency Scaling (DVFS) technique have been proposed both for CPUs and NoCs. The promise is to be a flexible and scalable way to jointly optimize power-performance, addressing both static and dynamic power sources. Being simulation a de-facto prime solution to explore novel multi-core architectures, a reliable full system analysis requires to integrate in the toolchain accurate timing and power models for the DVFS block and for the resynchronization logic between different Voltage and Frequency Islands (VFIs). In such a way, a more accurate validation of novel optimization methodologies which exploit such actuator is possible, since both architectural and actuator overheads are considered at the same time. This work proposes a complete cycle accurate framework for multi-core design supporting Global Asynchronous Local Synchronous (GALS) NoC design and DVFS actuators for the NoC. Furthermore, static and dynamic frequency assignment is possible with or without the use of the voltage regulator. The proposed framework sits on accurate analytical timing model and SPICE-based power measures, providing accurate estimates of both timing and power overheads of the power control mechanisms

A Control-based Methodology for Power-performance Optimization in NoCs Exploiting DVFS

Networks-on-Chip (NoCs) are considered a viable solution to fully exploit the computational power of multi- and many-cores, but their non negligible power consumption requires ad hoc power-performance design methodologies. In this perspective, several proposals exploited the possibility to dynamically tune voltage and frequency for the interconnect, taking steps from traditional CPU-based power management solutions. However, the impact of the actuators, i.e. the limited range of frequencies for a PLL (Phase Locked Loop) or the time to increase voltage and frequency for a Dynamic Voltage and Frequency Scaling (DVFS) modules, are often not carefully accounted for, thus overestimating the benefits. This paper presents a control-based methodology for the NoC power-performance optimization exploiting the Dynamic Frequency Scaling (DFS). Both timing and power overheads of the actuators are considered, thanks to an ad hoc simulation framework. Moreover the proposed methodology eventually allows for user and/or OS interactions to change between different high level power-performance modes, i.e. to trigger performance oriented or power saving system behaviors. Experimental validation considered a 16-core architecture comparing our proposal with different settings of threshold-based policies. We achieved a speedup up to 3 for the timing and a reduction up to 33.17% of the power ∗ time product against the best threshold-based policy. Moreover, our best control-based scheme provides an averaged power-performance product improvement of 16.50% and 34.79% against the best and the second considered threshold-based policy setting

Efficient abstraction of clock synchronization at the operating system level

Distributed embedded systems are emerging and gaining importance in various domains, including industrial control applications where time determinism – hence network clock synchronization – is fundamental. In modern applications, moreover, this core functionality is required by many different software components, from OS kernel and radio stack up to applications. An abstraction layer devoted to handling time needs therefore introducing, and to encapsulate time corrections at the lowest possible level, the said layer should take the form of a timer device driver offering a Virtual Clock to the entire system. In this paper we show that doing so introduces a nonlinearity in the dynamics of the clock, and we design a controller based on feedback linearization to handle the issue. To put the idea to work, we extend the Miosix RTOS with a generic interface allowing to implement virtual clocks, including the newly designed controller that we call FLOPSYNC-3 after its ancestor. Also, we introduce the resulting virtual clock in the TDMH [20] real-time wireless mesh protocol

Jitter-Compensated VHT and Its Application to WSN Clock Synchronization

Accurate and energy-efficient clock synchronization is an enabler for many applications of Wireless Sensor Networks. A fine-grained synchronization is beneficial both at the system level, for example to favor deterministic radio protocols, and at the application level, when network-wide event timestamping is required. However, there is a tradeoff between the resolution of a WSN node's timekeeping device and its energy consumption. The Virtual High-resolution Timer (VHT) is an innovative solution, that was proposed to overcome this tradeoff. It combines a high-resolution oscillator to a low-power one, turning off the former when not needed. In this paper we improve VHT by first identifying the jitter of the low-power oscillator as the current limit to the technique, and then proposing an enhanced solution that synchronizes the fast and the slow clock, rejecting the said jitter. The improved VHT is also less demanding than the original technique in terms of hardware resources. Experimental results show the achieved advantages in terms of accuracy

Reliability-oriented resource management for High-Performance Computing

Reliability is an increasingly pressing issue for High-Performance Computing systems, as failures are a threat to large-scale applications, for which an even single run may incur significant energy and billing costs. Currently, application developers need to address reliability explicitly, by integrating application-specific checkpoint/restore mechanisms. However, the application alone cannot exploit system knowledge, which is not the case for system-wide resource management systems. In this paper, we propose a reliability-oriented policy that can increase significantly component reliability by combining checkpoint/restore mechanisms exploitation and proactive resource management policies