The Model
Some jobs have a “real time constraint” or maximum slowdown.
The system makes a Quality of Service guarantee: The job will have slowdown less than the maximum slowdown.
The system can reject jobs as necessary to meet guarantees.
Sample Real Time Constraint
Notes:
We define a job’s real-time constraint or maximum slowdown as the largest slowdown permissible for that job. In other words, if we can theoretically complete a job in 10 seconds, and must complete it in 30 seconds, it has a maximum slowdown of 3. In accepting this job, we guarantee that the job will have a slowdown ? 3.
A system cannot meet real time demands unless it has the ability to reject jobs when necessary. To see this, consider a batch of n+1 jobs, each with maximum slowdown 1, submitted simultaneously. If we must accept all jobs, one machine receives two jobs, and violates two real-time constraints.