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.