Dynamical Model for a Real–Time Task
Pedro Guevara López1, J. J. Medel 2 y Daniel Cruz Pérez3
1 Centro de Investigación en Tecnologías de Información y Sistemas – UAEH Carretera Pachuca–Tulancingo km. 4.5 Ciudad Universitaria, México Hidalgo. pguevara@df1.telmex.net.mx
2 Centro de Investigación en Innovación Tecnológica – IPN Cerrada CECATI s/n. Col. Santa Catarina C.P. 02250 Azcapotzalco, D.F. jjmedel@pollux.cic.ipn.mx
3 Centro de Investigación en Computación – IPN Av. Juan de Dios Bátiz sn esq. Miguel Othón de Mendizábal C. P. 07738 México D. F., dcruzp@yahoo.com
]]> Artículo recibido en enero 21, 2004
Resumen
Las técnicas de planificación estáticas [1] parten de la hipótesis de que el conjunto de tiempos de arribo y de ejecución de las tareas se conocen a priori, mientras que las técnicas dinámicas [1] generalmente se basan en servidores de planificación; sin embargo, en ambos casos se desconoce el comportamiento real de la tarea y los arribos de sus respectivas instancias. Si se desconoce esta dinámica de las tareas no es posible hablar de predecibilidad. En este documento se propone un modelo dinámico general para tiempos de arribo, tiempos de ejecución y determinación de plazos basado en sistemas ARMA que incluyen el jitter y perturbaciones ajenas al procesador [3] y [13]. A través de éste modelo es posible definir el comportamiento de las tareas periódicas, esporádicas, y aperiódicas en un sentido de probabilidad.
Palabras Clave: Arribo, ejecución, modelo, plazo, Tiempo Real.
Abstract
Static scheduling techniques [1] are based on the hypothesis that the arrival times set and tasks execution times are known previously; while dynamical techniques [1] are generally based on scheduling servers. However, in both cases the real–time task behavior and their arrival times are unknown. It is impossible to talk about predictability without knowing those task dynamics. In this paper, we propose a dynamical model for arrival times and execution times, both based on ARMA models that include jitter and external perturbations of processor, in consequence deadlines are determined. With this model it is possible to know periodic, sporadic and aperiodic tasks behavior in a probability sense.
Keywords: Arrival, computation, model, deadline, Real–time.
]]>DESCARGAR ARTÍCULO EN FORMATO PDF
Referencias
1. Buttazzo G. (1997) Hard real–time computing systems. Scuola Superiore S. Anna, Kluwer Academic Publishers. [ Links ]
2. Medel J. J., Guevara P. "Constraints for real–time digital filters" Automatic Control and Computer Sciences AVT No. 5 pages 63–69 ISSN 0132–4160, September 2003, Latvia. [ Links ]
3. Jeffay K., Stanat D., Martel C. (1991). On non–preemptive scheduling of periodic and sporadic tasks. Proceedings of the Twelfth IEEE Real–Time Systems Symposium, San Antonio Texas. [ Links ]
4. Liu C., Layland J. (1973). Scheduling algorithms for multiprogramming in hard–real–time environment. Journal of the ACM, Vol. 20, No. 4, (1982), pp 273–250. [ Links ]
5. Rajkumar R. (1991). Synchronization in real–time systems, a priority inheritance approach. Kluwer Academic Publishers. [ Links ]
6. Martin J. (1980). Diseño de sistemas de computadores en Tiempo Real. Ed. Diana 1980. [ Links ]
7. Mok A., Chen D. (1997). A general model for real–time tasks. Technical report, University of Texas at Austin. [ Links ]
8. Ramanathan P., Kang D. (1994). A generalized guarantee model for servicing sporadic tasks with firm deadlines. Real–time Systems Journal May 1994. [ Links ]
9. Choi S., Agrawala A. (1997). Scheduling aperiodic and sporadic tasks in hard real–time systems. Technical report University of Maryland. [ Links ]
10. Burns A., Wellings A. "Real–time systems and programming languages ". University of York, Addison Wesley, 1997. [ Links ]
11. Abeni L., Buttazzo G. (1999). QoS Guarantee using probabilistic deadlines. Proceedings of the IEEE Euromicro Conference on Real–Time Systems, York, UK, June 1999. [ Links ]
12. Spuri M. & Buttazzo G. (1996). Scheduling aperiodic tasks in dynamic priority systems. Journal of real–time systems. [ Links ]
13. Guevara P, Medel J. J. (2002). Modelo ARMA para caracterización de tareas en tiempo real". Taller Internacional de Instrumentación Virtual CIC–INDI 2002, Pachuca agosto de 2002. [ Links ]
14. Medel J. J., Guevara P. (2002). Análisis Restrictivo para Filtros Digitales en Tiempo Real Presentando un Ejemplo para un SLIT tipo SISO. IBERAMIA 2002, Sevilla España. [ Links ]
15. J. K. Dey, James Kurose, Don Towsley (1993). Efficent On–Line Processor for a Class of IRIS (Increasing Reward with Increasing Service) Real–Time Tasks. SIGMETRICS 1993: 217–228. [ Links ]
16. Ash R. "Real Analysis and Probability", Ed. Academic Press, USA, 1970. [ Links ]
17. Nyquist H. "Certain Topics in Telegraph Transmission Theory". AIEE Transactions, USA 1928. [ Links ]
18. T. Abdelzaher, John Stankovic, Chenyang Lu, Ronghua Zhang, Ying Lu. (2003) "Feedback Performance Control in Sofware Services". [ Links ]
19. K. Jeffay, D. Becker D. Bennett "The Design, Implementation and Use of a Sporadic Task Model". [ Links ]
20. A. Adas, (1997) "Traffic Models in Broadband Networks". IEEE Communications, 35(7): 82––89, July 1997. [ Links ]
21. J. P. Lehoczky. (1996), "Real Time Queueing Theory". 17th IEEE Real–Time Systems Symposium (RTSS '96) December 04 – 06, 1996 Washington D.C. [ Links ]
22. Tia T., Deng Z., Shankar M., Storch M., Sun J., Wu L., Liu J. (1995). Probabilistic performance guarantee for real–time tasks with varying computation times. IEEE Real–time technology applications symposium. [ Links ] ]]>