Problem 11: Complex Hierarchical Scheduling

Full Processor

FP

T3T2

T4T1

EDF

T6T5

RM

T10T9T8T7

EDFSPS

DPS

10 Tasks - with jitter- with bursts- deadline = period- deadline < period- deadline > period- preemptive & independent

3 Scheduling Policies- Rate Monotonic- Earliest Deadline First- Fixed Priority

Hierarchical SchedulingStatic & Dynamic Polling Servers

Total Utilization: 98.5%

Schedulable?Min. req. processor speed?

Priority 1 Priority 4

Priority 3Priority 2

Real-Time Load Specification

pSPS = 4 (period) pDPS = 3 (period)eSPS = 1 (execution share) eDPS =1 (execution share)dSPS = 4 (deadline) dDPS = 3 (deadline)

Periodic Server

• A polling server can be thought of as a periodic task T (p, e). • When the server-task T is selected to run by the scheduler, the

server-task checks whether workload is waiting to be processed by the server.

• If yes, the server will provide e resources to process the waiting workload.

• If no work is available for the server, the task will immediately be finished, i.e. the server will not check for arriving work anymore until the next period starts.

• While the server is processing, it is preemptable. When it is preempted, it is put back into the ready-queue.

• If the server could not provide e resources during a time interval T, even though there was always enough work available, then this is treated the same as a deadline-miss. I.e. the system is considered to be not schedulable.