Using a lag-balance property to tighten tardiness bounds for global EDF

Several tardiness bounds for global EDF and global-EDF-like schedulers have been proposed over the last decade. These bounds contain a component that is explicitly or implicitly proportional to how much the system may be cumulatively lagging behind, in serving tasks, with respect to an ideal schedule. This cumulative lag is in its turn upper-bounded by upper-bounding each per-task component in isolation, and then summing individual per-task bounds. Unfortunately, this approach leads to an over-pessimistic cumulative upper bound. In fact, it does not take into account a lag-balance property of any work-conserving scheduling algorithm. In this paper we show how to get a new tardiness bound for global EDF by integrating this property with the approach used to prove the first tardiness bounds proposed in the literature. In particular, we compute a new tardiness bound for implicit-deadline tasks, scheduled by preemptive global EDF on a symmetric multiprocessor. According to our experiments, as the number of processors increases, this new tardiness bound becomes tighter and tighter than the tightest bound available in the literature, with a maximum tightness improvement of 29 %. A negative characteristic of this new bound is that computing its value takes an exponential time with a brute-force algorithm (no faster exact or approximate algorithm is available yet). As a more general result, the property highlighted in this paper might help to improve the analysis for other scheduling algorithms, possibly on different systems and with other types of task sets. In this respect, our experimental results also point out the following negative fact: existing tardiness bounds for global EDF, including the new bound we propose, may become remarkably loose if every task has a low utilization (ratio between the execution time and the minimum inter-arrival time of the jobs of the task), or if the sum of the utilizations of the tasks is lower than the total capacity of the system

Tight Tardiness Bounds for Pseudo-Harmonic Tasks Under Global-EDF-Like Schedulers

The global earliest-deadline-first (GEDF) scheduler and its variants are soft-real-time (SRT) optimal for periodic/sporadic tasks, meaning they provide bounded tardiness so long as the underlying platform is not over-utilized. Although their SRT-optimality has long been known, tight tardiness bounds for these schedulers have remained elusive. In this paper, a tardiness bound, that does not depend on the processor or task count, is derived for pseudo-harmonic periodic tasks, which are commonly used in practice, under global-EDF-like (GEL) schedulers. This class of schedulers includes both GEDF and first-in-first-out (FIFO). This bound is shown to be generally tight via an example. Furthermore, it is shown that exact tardiness bounds for GEL-scheduled pseudo-harmonic periodic tasks can be computed in pseudo-polynomial time

REAL-TIME SCHEDULING ON ASYMMETRIC MULTIPROCESSOR PLATFORMS

Real-time scheduling analysis is crucial for time-critical systems, in which provable timing guarantees are more important than observed raw performance. Techniques for real-time scheduling analysis initially targeted uniprocessor platforms but have since evolved to encompass multiprocessor platforms. However, work directed at multiprocessors has largely focused on symmetric platforms, in which every processor is identical. Today, it is common for a multiprocessor to include heterogeneous processing elements, as this offers advantages with respect to size, weight, and power (SWaP) limitations. As a result, realizing modern real-time systems on asymmetric multiprocessor platforms is an inevitable trend. Unfortunately, principles and mechanisms regarding real-time scheduling on such platforms are relatively lacking. The goal of this dissertation is to enrich such principles and mechanisms, by bridging existing analysis for symmetric multiprocessor platforms to asymmetric ones and by developing new techniques that are unique for asymmetric multiprocessor platforms. The specific contributions are threefold. First, for a platform consisting of processors that differ with respect to processing speeds only, this dissertation shows that the preemptive global earliest-deadline-first (G-EDF) scheduler is optimal for scheduling soft real-time (SRT) task systems. Furthermore, it shows that semi-partitioned scheduling, which is a hybrid of conventional global and partitioned scheduling approaches, can be applied to optimally schedule both hard real-time (HRT) and SRT task systems. Second, on platforms that consist of processors with different functionalities, tasks that belong to different functionalities may process the same source data consecutively and therefore have producer/consumer relationships among them, which are represented by directed acyclic graphs (DAGs). End-to-end response-time bounds for such DAGs are derived in this dissertation under a G-EDF-based scheduling approach, and it is shown that such bounds can be improved by a linear-programming-based deadline-setting technique. Third, processor virtualization can lead a symmetric physical platform to be asymmetric. In fact, for a designated virtual-platform capacity, there exist an infinite number of allocation schemes for virtual processors and a choice must be made. In this dissertation, a particular asymmetric virtual-processor allocation scheme, called minimum-parallelism (MP) form, is shown to dominate all other schemes including symmetric ones.Doctor of Philosoph

Valuing the Air: The Politics of Environmental Governance from the Clean Air Act to Carbon Trading

In 1970, the United States Congress and President Richard Nixon created a federal regulatory regime to meet public demands for improved environmental quality. As it happened, the formation of the Environmental Protection Agency (EPA) and the enactment of the first national environmental standards coincided with the disruption of the postwar prosperity that had helped fuel the environmental movement. Valuing the Air provides the first sustained historical study of policy making at EPA during the formative period between 1970 and 1990, when the embattled agency preserved its original mission to protect Americans’ right to clean air. To justify strong regulations in an era of rising inflation and unemployment, EPA officials turned to the new field of environmental economics, funding pioneering research that concluded that the benefits of environmental protection outweighed the costs. Such pecuniary evidence allowed EPA to shield its regulatory interventions from business lobbying and to rebut rhetorical campaigns in which corporate executives threatened communities across the country with the loss of industrial jobs if they supported strong environmental health regulations. While this dollars and cents valuation proved persuasive to policy makers, it ran contrary to environmentalist notions of priceless nature and environmental advocates fought doggedly to prevent EPA from fully adopting a cost/benefit approach to policymaking. As environmentalists recognized, EPA’s embrace of economic measurement elevated the stature of economists at the agency, raising the possibility that recently established natural rights to clean air and water might be undercut by a dehumanized pricing of externalities. Regulatory reforms enacted by the Carter administration, such as emissions trading and the bubble policy, signaled a new willingness among liberals to use economic incentives and markets approaches in place of direct regulations – a development that environmentalists regarded warily. In 1981, the Reagan administration upset a bipartisan consensus for market based reforms with the announcement of drastic budget and staffing cuts at EPA. Reagan’s attack on EPA marked the ascent of a new conservative ideology that held unrestrained free enterprise to be the greatest social good, irrespective of the actual economics of regulatory interventions. Finding environmental economics to be a powerful, if imperfect, ally against such assaults, many environmental organizations softened their critiques of economic valuation and began to borrow the language and logic of economics to make their case. With this growing support from environmental organizations, EPA ushered in the commodification of pollution rights in the era of cap and trade. The inflection of contemporary environmental advocacy with economic measurement and value demonstrates the political utility of economics while also underscoring the foreclosure of an earlier environmentalism’s more radical questioning of the desirability of an unbounded market economy. At the same time, EPA continues to resist economists’ efforts to derive public preferences from market exchange, insisting that fundamental choices about underlying environmental value be made through the democratic process

Fuelling the zero-emissions road freight of the future: routing of mobile fuellers

The future of zero-emissions road freight is closely tied to the sufficient availability of new and clean fuel options such as electricity and Hydrogen. In goods distribution using Electric Commercial Vehicles (ECVs) and Hydrogen Fuel Cell Vehicles (HFCVs) a major challenge in the transition period would pertain to their limited autonomy and scarce and unevenly distributed refuelling stations. One viable solution to facilitate and speed up the adoption of ECVs/HFCVs by logistics, however, is to get the fuel to the point where it is needed (instead of diverting the route of delivery vehicles to refuelling stations) using "Mobile Fuellers (MFs)". These are mobile battery swapping/recharging vans or mobile Hydrogen fuellers that can travel to a running ECV/HFCV to provide the fuel they require to complete their delivery routes at a rendezvous time and space. In this presentation, new vehicle routing models will be presented for a third party company that provides MF services. In the proposed problem variant, the MF provider company receives routing plans of multiple customer companies and has to design routes for a fleet of capacitated MFs that have to synchronise their routes with the running vehicles to deliver the required amount of fuel on-the-fly. This presentation will discuss and compare several mathematical models based on different business models and collaborative logistics scenarios

Bowdoin Orient v.133, no.1-25 (2001-2002)

https://digitalcommons.bowdoin.edu/bowdoinorient-2000s/1002/thumbnail.jp