Low Power Design for Real-Time Systems

Low power (energy) consumption is a key design for embedded systems Battery’s life during operation Reliability Size of the system

Power-aware real-time scheduling Minimize the energy consumption while satisfying the

real-time constraints.

Dynamic Voltage Scaling (DVS) Technique for Real-Time Task CPU’s energy/power consumption is a convex function of the

CPU’s speed, e.g. P = CV2f -> P = s3. Slowing down CPU’s speed reduces the energy usage for CPU. Saving energy consumption v.s. Meeting deadline.

Reducing the CPU’s speed as much as possible while meeting every task’s deadline.

A minimum constant speed is always an optimal solution (if possible).

If more than one speed are needed, a “smooth” selection is better.

For regular single instance real-time jobs with only one feasible interval, Yao designed an algorithm for computing the optimal solution.

Considering power consumption for leakage current As VLSI technology marches towards deep

submicron and nanoscale circuits operating at multi-GHz frequencies, the rapidly elevated leakage power dissipation will soon become comparable to, if not exceeding, the dynamic power consumption:Pleak = I leak V

P = Pdyn + Pleak

A critical speed s* = s where P(s) = P’(s)sShut down the CPU when it is idle.

• Shut-down overhead.

RealEnergy: a New Framework and Tool to Evaluate Power-Aware Real-Time Scheduling Algorithms

Linux

Measure EnergyTarget System

ApplicationsBenchmarks

RTAI

Data Analysis

Low Power Scheduling

Alg.

Change Frequency

CPU Sleep & Wake-up

Intel XScale/PXA255 Module

Example of the Measured Current

using RealEnergy

Actual Energy Consumption Using DVS as meaured by RealEnergy

References J. Lin and A. M. K. Cheng, “Real-time Task Assignment in Recharegable

Multiprocessor Systems,” Proc. 14th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA), Kaohsiung, Taiwan, Aug. 2006.

J. Lin and A. M. K. Cheng, ``Real-time Task Assignment in Heterogeneous Distributed Systems with Rechargeable Batteries,'' IEEE International Conference on Advanced Information Networking and Applications (AINA), Bradford, UK, May 26-29, 2009.

J. Lin and A. M. K. Cheng, ``Power-aware scheduling for Multiple Feasible Interval Jobs,'' Proc. 15th IEEE-CS International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA), Beijing, China, Aug. 2009. Nominated for Best Paper Award.

J. Lin, W. Song, A. M. K. Cheng ``RealEnergy: a New Framework and a Case Study to Evaluate Power-Aware Real-Time Scheduling Algorithms ,'' to appear in ACM International Symposium on Low Power Electronics and Design (ISLPED), Austin, Texas, USA, August 18-20, 2010.