SYSC_3303_Real_Time_Scheduling.15

SYSC_3303_Real_Time_Scheduling.15 - SYSC 3303 Real-Time...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
1 SYSC 3303 Real-Time Concurrent Systems Scheduling Schemes for Real-Time Systems Copyright © 2003 D.L. Bailey and L.S. Marshall, Systems and Computer Engineering, Carleton University revised July 30 th , 2003
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
SYSC 3303 - Scheduling Schemes for Real-Time Systems 2 Correctness of Concurrent Programs • In a non-real-time concurrent system, as long as the algorithms in each process are implemented correctly, and as long as the required mutual exclusion and condition synchronization are correctly programmed, the outputs of the program will be the same regardless of the order in which the processes are executed – in these slides, the terms process and thread are synonymous • As long as the program's outputs are correct, the timing behaviour is not a major issue • Real-time systems are different
Background image of page 2
SYSC 3303 - Scheduling Schemes for Real-Time Systems 3 What is a Real-Time System? • “A real-time system must respond to unpredictable stimuli from its environment in a timely fashion while operating reliably and continuously in the presence of failures in its own (perhaps distributed) components and connections, and uncertainty about the state of its environment.”
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
SYSC 3303 - Scheduling Schemes for Real-Time Systems 4 Hard vs. Soft Real-Time Hard real-time system - responses must occur within specified deadlines – the system fails if its deadlines are missed, and this failure can have catastrophic results Soft real-time system - response times are important, but system functions correctly if a deadline is occasionally missed (e.g., responses occasionally delivered late or not at all) • In comparison, a system is called interactive if it does not have specified deadlines but attempts to provide "adequate" response times
Background image of page 4
SYSC 3303 - Scheduling Schemes for Real-Time Systems 5 Process Scheduling in R-T Systems • In other words, real-time systems have temporal requirements in addition to their other requirements • Processes in a real-time system must be scheduled so that the system meets its temporal requirements • A scheduling scheme provides – an algorithm for ordering the use of system resources (especially the CPU(s)) – a means of predicting the worst-case behaviour of the system when the scheduling algorithm is applied
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
SYSC 3303 - Scheduling Schemes for Real-Time Systems 6 What We've Seen So Far • Earlier in the course, we discussed prioritized, preemptive scheduling, and mechanisms for controlling priority inversion (priority inheritance protocol, priority ceiling protocol), but our descriptions were qualitative in nature • Now we'll go back to first principles, and provide a quantitative description of various scheduling schemes • To simplify the analysis of the worst-case system behaviour, we'll initially use a very simple process model when presenting some standard scheduling schemes
Background image of page 6
SYSC 3303 - Scheduling Schemes for Real-Time Systems 7 A Simple Process Model • The program consists of a fixed set of processes • All processes are periodic, with known periods
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 34

SYSC_3303_Real_Time_Scheduling.15 - SYSC 3303 Real-Time...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online