Modern DRAM Memory Systems: Performance Analysis and Scheduling Algorithm

The performance characteristics of modern DRAM memory systems are impacted by two primary attributes: device datarate and row cycle time. Modern DRAM device datarates and row cycle times are scaling at different rates with each successive generation of DRAM devices. As a result, the performance characteristics of modern DRAM memory systems are becoming more difficult to evaluate at the same time that they are increasingly limiting the performance of modern computer systems. In this work, a performance evaluation framework that enables abstract performance analysis of DRAM memory systems is presented. The performance evaluation framework enables the performance characterization of memory systems while fully accounting for the effects of datarates, row cycle times, protocol overheads, device power constraints, and memory system organizations. This dissertation utilizes the described evaluation framework to examine the performance impact of the number of banks per DRAM device, the effects of relatively static DRAM row cycle times and increasing DRAM device datarates, power limitation constraints, and data burst lengths in future generations of DRAM devices. Simulation results obtained in the analysis provide insights into DRAM memory system performance characteristics including, but not limited to the following observations. The performance benefit of having a 16 banks over 8 banks increases with increasing datarate. The average performance benefit reaches 18% at 1 Gbps for both open-page and close-page systems. Close-page systems are greatly limited by DRAM device power constraints, while open-page systems are less sensitive to DRAM device power constraints. Increasing burst lengths of future DRAM devices can adversely impact cache-limited processors despite the increasing bandwidth. Performance losses of greater than 50% are observed. Finally, This dissertation also present a unique rank hopping DRAM command-scheduling algorithm designed to alleviate the bandwidth constraints in DDR2 and future DDRx SDRAM memory systems. The proposed rank hopping scheduling algorithm schedules DRAM transactions and command sequences to avoid the power limiting constraints and amortizes the rank-to-rank switching overhead. Execution based simulations show that some workloads are able to fully utilize the additional bandwidth and significant performance improvements are observed across a range of workloads

Transportation evacuation strategies based on vehicular disaster management system in urban network environment Zubaida

The importance of emergency response systems have grown tremendously in the recent times due to the many manmade and natural disasters in recent years such as September 2001, July 2005 London bombings and the 2011 Japan earthquake and tsunami disaster. Disasters cost huge human, social and financial losses. For example, in Typhoon Haiyan, as of November 2013, the official death toll from Philippines‟s devastating storm has passed 10,000 people. In addition, based on early estimates, the reconstruction costs could come to as much as $20bn (£12.3bn). Conventional methods for disaster management have shown little prospects of realizing the true potential of current and emerging technologies.This PhD research aims to propose and evaluate a disaster management system based on the emerging ICT technologies with a focus on transportation in urban environments. This work is presented on an Intelligent Disaster Management System based on Vehicular Ad hoc Networks (VANETs) and Cloud Computing. Our research objective is to increase the safety and system efficiency, to reduce the accidents, congestion, and manage the emergencies and disasters. The effectiveness of the intelligent system has been demonstrated through modelling the impact of disaster on real city transport environments and compares it with the case where the intelligent proposed system was in place, and ability of generalizing the concept was increased through applying the proposed system on different cities. By applying our system, substantial benefits have been achieved in terms of improved and balanced traffic flow and smooth evacuation rates.Furthermore, a micro-simulation software model has been developed which employs the vehicular disaster management system in order to investigate the transportation evacuation strategies potential in reducing the human and economic losses.The particular contribution of my thesis is in the modelling and simulation of the traffic for disaster and evacuation scenarios. To this end, this project uses a range and mix of modelling and simulation technologies including macroscopic and microscopic simulation models; OmniTRANS and S-Paramics transport planning software.xixDuring the course of this PhD, disaster scenarios of varying scales involving 2-3 different cities of various sizes and characteristics have been modelled and analysed, thereby presenting a system which deliver advanced services in managing disasters which results in lower losses.Also, the Average Vehicle Occupancy impact on the evacuation process time has been investigated. Literally, it represents the higher number of car occupancy which means less number of trips required to the evacuation process. The results have shown that AVO contributes effectively in evacuation plans that are in place.Additionally, two different evacuation strategies have been applied and evaluated simultaneously and isolated. Subsequently, either continues the processes or perhaps there is a need to change the strategy where applicable and appropriate. In other words, after propagating the evacuation strategy, the traffic situation has been assessed and observed the effectiveness of the disaster management system on the network by comparing the performance of the proposed system against the traditional system. To sum up, the comparison between both scenarios shows the ability to secure more of vehicles, up to double the number, and hence improve the network performance in terms of safety. Moreover, there is an improvement in flow rate of many critical links. Many blocked links are turned into some reds and blues which means an improvement seemed to occur to the whole network