A constant utilization server gives a known fraction of processor capacity to a task but cannot claim unused capacity to complete the task earlier.
A total bandwidth server improves responsiveness by allowing a server to claim background time not used by the periodic tasks.
This is done by having the scheduler replenish the server budget as soon as the budget is exhausted if the server is backlogged at the time or as soon as the server becomes backlogged.
- A total bandwidth server only consumes budget when it Replenishment Rule:
- Initially, e s = 0 and d = 0
- When an aperiodic job with execution time e arrives at time t to an empty aperiodic job queue
- Set d = max(d, t ) + e/ũ s and e s = e
- When the server completes the current aperiodic job, the job is removed from the queue then
- If the server is backlogged, set d = d + e/ũ s and e s = e
- If the server is idle, do nothing
Total bandwidth server is always ready for execution when backlogged and assigns at least fraction ũ s of the processor to a task foe execution.
For example: ũ s = 0.25 T1 = (3, 0.5), T2 = (4, 1), T3 = (19, 4.5)