13 research outputs found
Satisfying hard real-time constraints using COTS components
L'utilizzo di componenti COTS (Commercial-Off-The-Shelf) è sempre più comune
nella produzione di sistemi embedded real-time. Prodotti commerciali, come periferiche di
Input/Output e bus di sistema, vengono utilizzati in sistemi real-time al fine
di ridurre i costi, il tempo di produzione, ed aumentare le performance.
Sfortunatamente, hardware e sistemi operativi COTS sono progettati
principalmente per ottimizzare le performance, ma con poca attenzione verso
determinismo, predicibilità ed
affidabilità . Per questa ragione, molte problematiche devono ancora essere
affrontate prima di un loro impiego in sistemi real-time ad alta criticita'.
In questa tesi abbiamo centrato la nostra attenzione su alcune delle piu' importanti
sorgenti di impredicibilita' che devono essere rimosse al fine di integrare
hardware e software COTS in sistemi hard real-time. Come prima cosa abbiamo sviluppato
ASMP-Linux, una variante di Linux che minimizza overhead e latenza del sistema
operativo. Successivamente abbiamo progettato ed implementato un nuovo sistema
di gestione dell'I/O, basato sul Real-Time Bridge, un nuovo componente
hardware che fornisce isolamento temporale sui bus COTS e rimuove le
interferenze fra periferiche di I/O. E' stato anche sviluppato un Multi-Flow
Real-Time Bridge per assicurare predicibilita' nel caso di periferiche
condivise. Infine abbiamo proposto PREM, un nuovo modello di esecuzione per
sistemi real-time che elimina le interferenze fra periferiche e CPU, e quelle
fra processi ad alta criticita' ed interruzioni hardware.
Per ognuna delle nostre soluzioni saranno descritti in dettaglio gli aspetti
teorici, l'implementazione dei prototipi ed i risultati sperimentali.Real-time embedded systems are increasingly being built using Commercial Off-The-Shelf (COTS) components such as mass-produced peripherals and buses to reduce costs, time-to-market, and increase performance. Unfortunately, COTS hardware and operating systems are typically designed to optimize average performance, instead of determinism, predictability, and reliability, hence their employment in high criticality real-time systems is still a daunting task.
In this thesis, we addressed some of the most important sources of unpredictability which must be removed in order to integrate COTS hardware and software into hard real-time systems. We first developed ASMP-Linux, a variant of Linux, capable of minimizing both operating system overhead and latency. Next, we designed and implemented a new I/O management system, based on real-time bridges, a novel hardware component that provides temporal isolation on the COTS bus and removes the interference among I/O peripherals. A multi-flow real-time bridge has been also developed to address interperipheral interference, allowing predictable device sharing. Finally, we propose PREM, a new execution model for real-time systems which eliminates interference between peripherals and the CPU, as well as interference between a critical task and driver interrupts. For each of our solutions, we will describe in detail theory aspects, as well as prototype implementations and experimental measurements
Effects of Communication Protocol Stack Offload on Parallel Performance in Clusters
The primary research objective of this dissertation is to demonstrate that the effects of communication protocol stack offload (CPSO) on application execution time can be attributed to the following two complementary sources. First, the application-specific computation may be executed concurrently with the asynchronous communication performed by the communication protocol stack offload engine. Second, the protocol stack processing can be accelerated or decelerated by the offload engine. These two types of performance effects can be quantified with the use of the degree of overlapping Do and degree of acceleration Daccs. The composite communication speedup metrics S_comm(Do, Daccs) can be used in order to quantify the combined effects of the protocol stack offload. This dissertation thesis is validated empirically. The degree of overlapping Do, the degree of acceleration Daccs, and the communication speedup Scomm characteristic of the system configurations under test are derived in the course of experiments performed for the system configurations of interest. It is shown that the proposed metrics adequately describe the effects of the protocol stack offload on the application execution time. Additionally, a set of analytical models of the networking subsystem of a PC-based cluster node is developed. As a result of the modeling, the metrics Do, Daccs, and Scomm are obtained. The models are evaluated as to their complexity and precision by comparing the modeling results with the measured values of Do, Daccs, and Scomm. The primary contributions of this dissertation research are as follows. First, the metric Daccs and Scomm are introduced in order to complement the Do metric in its use for evaluation of the effects of optimizations in the networking subsystem on parallel performance in clusters. The metrics are shown to adequately describe CPSO performance effects. Second, a method for assessing performance effects of CPSO scenarios on application performance is developed and presented. Third, a set of analytical models of cluster node networking subsystems with CPSO capability is developed and characterised as to their complexity and precision of the prediction of the Do and Daccs metrics