Abhilash Thekkilakattil, Radu Dobrin, Sasikumar Punnekkat Mälardalen Real-time Research Center, Mälardalen University Västerås, Sweden Towards Preemption Control using CPU Frequency Scaling in Sporadic Task Systems

Real-time scheduling paradigms Non-preemptivePreemptive Low runtime overhead  Increased blocking times Ability to achieve high utilization  Preemption costs How to take advantage of both paradigms? Dynamic Voltage (and Frequency) Scaling Speed up or slow down task executions Supported by most modern processors Traditionally used to slow down task executions : energy conservation Applying frequency scaling for preemption control in a sporadic task system Our work:

Preemption control algorithm: example C= = 12 Max. time available= 4 - 1= 3 C = 2 Max. time available= 10 – 8 = Task A B C D Rate monotonic schedule ModesM1M2M3M4M5M6 Speed S = 12/3=4 S = 2/2 =1 Exec. TimePeriod Processor modes C = 2 Max. time available= 10 – 17 = -7 S = 6 C = 6 Max. time available=24 – 21 = 3 S = 6/3 = 2 C = 2 Max. time available= 24 – 25 = -1 S = 6 C = 2 Max. time available= 40 – 38 = 2 S = 1

Preliminary evaluations

Conclusions and future work Method to control preemption behavior in real time systems using CPU frequency scaling –Online : linear complexity –Provides for trade-off between preemptions and energy consumption –Required no modifications to task attributes –Main element of cost: energy On going effort: –Optimality –Competitive analysis –Comparison with other approaches

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