Optimal Selection of Preemption Points to Minimize Preemption Overhead

A central issue for verifying the schedulability of hard real-time systems is the correct evaluation of task execution times. These values are significantly influenced by the preemption overhead, which mainly includes the cache related delays and the context switch times introduced by each preemption. Since such an overhead significantly depends on the particular point in the code where preemption takes place, this paper proposes a method for placing suitable preemption points in each task in order to maximize the chances of finding a schedulable solution. In a previous work, we presented a method for the optimal selection of preemption points under the restrictive assumption of a fixed preemption cost, identical for each preemption point. In this paper, we remove such an assumption, exploring a more realistic and complex scenario where the preemption cost varies throughout the task code. Instead of modeling the problem with an integer programming formulation, with exponential worst-case complexity, we derive an optimal algorithm that has a linear time and space complexity. This somewhat surprising result allows selecting the best preemption points even in complex scenarios with a large number of potential preemption locations. Experimental results are also presented to show the effectiveness of the proposed approach in increasing the system schedulability

Optimal Selection of Preemption Points to Minimize Preemption Overhead

Abstract—A central issue for verifying the schedulability of hard real-time systems is the correct evaluation of task execution times. These values are significantly influenced by the preemption overhead, which mainly includes the cache related delays and the context switch times introduced by each preemption. Since such an overhead significantly depends on the particular point in the code where preemption takes place, this paper proposes a method for placing suitable preemption points in each task in order to maximize the chances of finding a schedulable solution. In a previous work, we presented a method for the optimal selection of preemption points under the restrictive assumption of a fixed preemption cost, identical for each preemption point. In this paper, we remove such an assumption, exploring a more realistic and complex scenario where the preemption cost varies throughout the task code. Instead of modeling the problem with an integer programming formulation, with exponential worst-case complexity, we derive an optimal algorithm that has a linear time and space complexity. This somewhat surprising result allows selecting the best preemption points even in complex scenarios with a large number of potential preemption locations. Experimental results are also presented to show the effectiveness of the proposed approach in increasing the system schedulability.

ICT tools for enhancing sustainable water management in rural environments

Numerical models are relevant tools to achieve the proper application of the Water Framework Directive (WFD, EU 2000). Their major advantage is to foster a full characterization of the involved flow terms and contaminant transport pathways. Thanks to their predictive function, numerical models can help also to address planning and management activities. Many hydrological codes developed so far have faced the problem of tackling multiscale territorial planning (e.g., Bergez et al. 2012). We introduce here the GIS-integrated FREEWAT platform aimed at providing a unique modeling environment to simulate multiple hydrological processes, with a focus on the sustainable management of conjunctive use of surface- and ground-water resources in rural environments. FREEWAT (FREE and open source software tools for WATer resource management; Rossetto et al., 2015) is an EU HORIZON 2020 project, whose main goal is to simplify the application of EU water-related Directives. It aims at integrating a simulation platform in a Geographic Information System (GIS), coupling the power of GIS geo-processing and post-processing tools in spatial data analysis to that of simulation codes. The FREEWAT platform is being developed within the QGIS free open source software package and fosters the simulation of the whole hydrological cycle using open source numerical codes mainly belonging to the USGS MODFLOW family

Minimizing end-to-end response time in transactions ∗ Enrico Bini

Many applications are today implemented by chains of tasks (called transactions) that require to execute on several computational nodes. When more than one task are allocated on the same node, it is necessary to assign properly the available computational resource to each task. In this paper we show that the rule of thumb of assigning an amount of resource proportional to the task computation time does not minimize the end-to-end response time. We derive instead the optimal resource assignment.