Esta tesis se ha centrado en el estudio de las políticas basadas en la
extracción de holgura y en la asignación dual de prioridades, ambas orientadas
a dar servicio a tareas aperiódicas en sistemas real estricto. Estas políticas
constituyen una interesante alternativa a las políticas basadas en servidores
de carga aperiódicas y han sido ampliamente estudiadas en numerosos trabajos.
No obstante, la posibilidad de ser aplicables en la práctica todavía no
había sido evaluada en detalle, y éste ha sido el principal objetivo de
esta tesis.
En este trabajo, ambas políticas son revisadas en profundidad. En el caso
de la política basada en la extracción de holgura, algunas de sus principales
debilidades han sido corregidas. En particular, se muestra que es posible
compartir recursos entre tareas críticas y aperiódicas de una forma sencilla
y eficiente, utilizando para ello los mismos protocolos de herencia de
prioridad que pueden aplicarse en sistemas en los que sólo existen tareas
críticas.
La aplicabilidad de estas políticas ha sido valorada incorporándolas en
los dos entornos más relevantes hoy en día para la programación de sistemas
de tiempo real estricto, el lenguaje de programación Ada y los servicios
POSIX. Con este fin se han definido nuevas interfaces para ambas políticas
en estos entornos, coherentes con sus principios de diseño y con los servicios
que actualmente ofrecen. El diseño de estas interfaces ha supuesto una
adaptación de ambas políticas buscando, en todo momento, un equilibrio
entre prestaciones y eficiencia. Como parte de este diseño, estas interfaces
han sido implementadas en el sistema operativo MaRTE OS. El proceso de
implementación ha servido para validar las distintas alternativas qu ehan
sido consideradas.
Un aspecto importante de una política de planificación en su eficiencia,
por lo que este aspecto ha sido evaluado en detalle. Se ha caracterizado
de forma analítica el efecto / ABSTRACT: This thesis is centered on the study of slack stealing and dual priority scheduling
policies, both oriented to serve aperiodic tasks in hard real-time systems. These polices,
largely studied in previous work, constitute an interesting alternative to policies based on
aperiodic servers. However, the possibility of actually being put into practice had not been
yet exhaustively evaluated. This has been the main objective of this thesis.
Both policies are profoundly revised in this dissertation. In the case of the slack stealing
policy, some of its weaknesses have been solved. In particular, this thesis shows that
it is possible to share resources between hard and aperiodic tasks in a simple and efficient
manner. This can be done by using the same priority inheritance protocols which are used
in systems comprising hard tasks only.
The applicability of these scheduling policies has been evaluated by means of their
incorporation into the two most relevant hard real-time programming environments in
use nowadays, the Ada programming language and the POSIX set of services. In order
to fulfill this purpose, new interfaces for both policies have been defined in these two
environments. These interfaces have been designed in order to be coherent with the environments¿
design principles and the services they currently support. This design has
involved the adaptation of the original scheduling policies, trying to optimize the balance
between performance and efficiency. As a part of this design, both interfaces have been
implemented in the MaRTE OS operating system. These implementations have been useful
for validating the different alternatives which have been considered throughout the
design process.
Since efficiency is an important aspect of any scheduling policy, this aspect has been
extremely evaluated in this work. The effect of the implementation of both policies to the
task response times has been analytically characterized. This effect has also been quantified,
and then the efficiency of both policies has been compared with the fixed-priority
preemptive scheduling policy, which is the one normally used in hard real-time systems.
The results of this comparative study show that, although the overhead introduced by any
VIII ABSTRACT
of the two new policies is significant, this overhead lies in a reasonable range.
The recently approved POSIX trace services have also been studied in this thesis.
The necessity of having some analysis and measurement tools available for the efficiency
studies carried out in this thesis led to the incorporation of these services into MaRTE OS.
Related to this, a new POSIX/Ada interface for the trace services has also been proposed.
In addition, the problem of obtaining temporal metrics of the system from the information
of the traces has also been covered. / Espinosa Minguet, AR. (2003). EXTENSIONES AL LENGUAJE ADA Y A LOS SERVICIOS POSIX PARA PLANIFICACIÓN EN SISTEMAS DE TIEMPO REAL ESTRICTO [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/17743
| Identifer | oai:union.ndltd.org:upv.es/oai:riunet.upv.es:10251/17743 |
| Date | 07 November 2012 |
| Creators | Espinosa Minguet, Agustín Rafael |
| Contributors | García Fornes, Ana María, Crespo Lorente, Alfons, Universitat Politècnica de València. Departamento de Sistemas Informáticos y Computación - Departament de Sistemes Informàtics i Computació |
| Publisher | Universitat Politècnica de València |
| Source Sets | Universitat Politècnica de València |
| Language | Spanish |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/acceptedVersion |
| Source | Riunet |
| Rights | http://rightsstatements.org/vocab/InC/1.0/, info:eu-repo/semantics/openAccess |
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