2 - Overview: Hard vs. Soft Real Time OUTLINE Timing...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
OUTLINE • Timing parameters for RT systems • Hard vs. soft timing constraints - soft real time systems - hard real time systems • CPU utilization • Validating timing constraints Overview: Hard vs. Soft Real Time Overview: Hard vs. Soft Real Time Ref: [Liu] • Ch. 2 (pg. 26 – 33) Timing parameters for RT Systems 2 Timing parameters: - Release Time (r) : time when job becomes available for execution. - Completion Time (f) : time when job finishes execution. - Response Time :( f – r ) - Deadline (d) : time when execution must be completed ( f d in R-T systems). - Relative Deadline (D) : maximum response time ( D = d – r ). - Execution time (e) : ( e f – r ) equals response time when processor is kept continuously busy. - Feasible interval of a job: time interval from r to d. red parameters are (usually) known to the scheduler before jobs are released, blue parameters are known only after the job has finished execution.
Background image of page 1

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

View Full DocumentRight Arrow Icon
Timing parameters for RT Systems (2) Timing parameters for RT Systems (2) 3 Other timing parameters: Lateness (L) : L = f – d ( L > 0 if deadline is not met) Tardiness (E) : E = max{ L , 0} ( E = 0 if deadline is met) Laxity ( Slack ): S(t) = d – t – e rem In the feasible interval of a job: - at time t , S(t) indicates the remaining time before the deadline ( d – t ) minus the remaining execution time ( e rem ). Slack time (laxity) Slack time (laxity) 4 S(t) = d – t – e rem the slack of a job is function of time defined in its feasible interval - at the release time r , S(r) ±= ±D ±–e ±=±d ±–r ± - S(t) remains constant when the job is executing - S(t) decreases with t when the job is not executing -if S(t) becomes negative, the deadline will be missed.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 8

2 - Overview: Hard vs. Soft Real Time OUTLINE Timing...

This preview shows document pages 1 - 3. Sign up to view the full document.

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