Other deadline assignment criteria
LSF Scheduling
Least Slack First : Executes first the task with smaller slack (Li (t)=di −ci (t))
LSF vs EDF short comparison.
LS is optimal (as EDF)
As the slack ↑ the priority ↓
Priority of ready tasks increases as time goes by.
Rescheduling only on instants where there are activations or terminations.
Priority of the task in the running state does not change.
In EDF the priorities of all tasks (ready and executing) increase equally as time goes by.
Causes an higher number of preemptions than EDF (and thus higher overhead).
No significant advantages with respect to EDF!
Example
FCFS Scheduling
Execute tasks as they arrive. Priority depends on the arrival order. A brief comparison between FCFS and EDF/LLF.
Non optimal.
May lead to deadline misses even with very low CPU utilization rates.
Job age ↑ Priority ↑
Priority of the ready and running tasks increases as time goes by (an in EDF).
New jobs always get the lower priority.
There are no preeemptions (smaller overhead and facilitates the implementation).
Very poor temporal behavior!
Example
When the “age” is the same the tie break criteria is decisive!
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