Power Modeling and Power Management Framework

Dexin Li

December 2002

Outline

• Background

• Power management architecture

• Component-level power modeling

• System-level power simulation

• Energy optimization

• Preliminary results

Background

• Challenges on power management in complex embedded systems– Interaction and cooperation among multiple components – Existence of inter-component dependencies– Complicated local mode transitions for a global mode change– High cost for a global mode change

• Scope of the work– Purpose a software architecture dealing with power management

complexity – Model components and component modes with dependency– Generate feasible sequence of mode transitions– Optimize the energy for the cost of mode changes

Power Management Architecture

• Separation of policy-maker and component details– Modular, retargetable, – Lessen the burden of policy-maker

• Hierarchical component model– Capable of handling complex systems

• Modeling of inter-component dependency– Enabling complicated mode transition optimization

• Online or offline power simulation– Helpful in obtaining feasible mode transitions and

optimizing system energy

Execution Model of Power Management

Hardware device

Operating System

Middle-ware

Application

Power manager

We assume this model in the rest of the presentation.

Top-Level Power Manager

Power Manager

Requirements

Device status

OS/MW status

System spec

Component library

Power simulator

External policy

App. status

Interdependency

Task constraint

Power/battery status

Control command

app

os

hw

Message to app.

Message to os

Decoupled Power Management Architecture Diagram

Policy Handler

C1 C2 Cn

Device Driver

C1 C2 Cn

Hardware Platform

ModeTransition

Graph

ModeDependency

Model

DPMA

ComponentSoftware

ModelComponent

Manager

Policy Handler

• Responsibilities– monitor system status– Make system-level power management policies– Send mode change commands

• System interaction – Accept service requests from applications– Accept system requirement or environment input from

middle-ware– Obtain system status from middle-ware or OS– Send mode change commands to Component Manager

Component Manager

• Command Interpreter– Receive system command from policy handler– Translate system command into local command

• Core algorithms– Generate sequence of mode transitions– Optimize it for energy reduction– Send results to device drivers– Feed results to simulation engine

CommandInterpreter

CoreAlgorithms

GlobalCommand

DeviceDriver

SimulationEngine

Component Manager

Component Manager Diagram

MTG 1

MTG 2

MTG n

ModeDependency

Model

Device status

System status CommandInterpreter

CoreAlgorithms

Policy Handler

Device driver

Component Manager

Component Modeling Example: Power Amplifier

Device status

System status

Command Interpreter

All-pair-shortest-path Algo.(Floyd-Warshall)

Component manager for PA

off sb

tx

rxf1: fsm_lb

off sb

tx

rxf2: fsm_hb

off on

f3: temp_lb

off on

f4: temp_hb

F1.sb->f2.offF1.tx->f2.offF1.rx->f2.offF2.sb->f1.offF2.tx->f1.offF2.rx->f1.offF1.sb->f3.onF1.tx->f3.onF1.rx->f3.onF2.sb->f4.onF2.tx->f4.onF2.rx->f4.on

Dependency model

Component Manager Example: Power Amplifier

off sb

tx

rxf1: fsm_lb

off sb

tx

rxf2: fsm_hb

Current state: low band transmit

System command: change to high band receive

State transition sequence:f1.tx -> f1.sb -> f1.offf2.off -> f2.sb -> f2.rxf4.off -> f4.on

off on

f4: temp_hb

Optimized for energy reduction:f1.tx -> f1.sb -> f1.offf4.off -> f4.onf2.off -> f2.sb -> f2.rx

Energy:3.88J

Energy:1.88J

System-level Mode Simulation

• Responsibility– Receive sequence of mode transitions – Simulate mode transitions– Parallelize possible mode transitions– Obtain time and energy information– Send the information back to Policy Handler

• Requirement– Detailed timing information for synchronization– Hierarchical component management– Parallelism among different components– Interface to other power management units

Simulation Engine Diagram

Controller

Monitor

Simulation Engine

off stb onf1

off stb on

off stb on

f2

fn

FromCore Algorithm

TOPolicy

Handler

Energy Optimization

• Objective– Optimize energy consumption for mode changes

• Techniques– Shortest-path algorithm to optimize for one mode

change on one component

– Topological sorting to power up high power component as late as possible

– Mode simulation to parallelize certain mode changes

Modeling a JTRS Channel

• Complex system composition– 13 power manageable components

– Multiple power modes on each component

• Complicated inter-component dependencies – derived from system specification and application

requirements

• Complicated mode changes– Involve more than one component for a mode change

– Take a period of time comparable to the service time

Experimental Results

• Test cases:– Case 1: all power-up– Case 2: two modes: on and off– Case 3: 5 system modes without

our model– Case 4: 5 system modes with our

modes

• Results:– Saves 50%-80% energy when

service time is comparable to overhead time

– Saves 20%+ energy when service time is 1000x larger than overhead time

Conclusion

• A new software architecture supporting efficient power management in complex systems

• Component power model enabling power management in complex systems with dependency

• Multiple optimization techniques reducing energy cost for global mode changes

• System-level simulation providing optimized component-level details to global policy-maker

End Slide

Execution Model of the Power Manager

Not clear what execution model is best/feasible/practical…

Hardware device

Operating System

Middle-ware

Application

Power manager

Device Broker

MTG 1

MTG 2

MTG n

ModeDependency

Model

Device status

System status Commandreceiver/

interpreter

Broker core

System power manager

Device driver

Mode Transition Graph

off stb

tx

rx

Execution Model of the Power Manager

Not clear what execution model is best/feasible/practical...

Hardware device

Operating System

Middle-ware

Application

Power manager

Execution Model of the Power Manager

Not clear what execution model is best/feasible/practical…

Hardware device

Operating System

Middle-ware

Application

Power manager

Execution Model of the Power Manager

Not clear what execution model is best/feasible/practical…

Hardware device

Operating System

Middle-ware

Application Power manager

More Detailed Power Manager Composition

Power Manager (core)Component

librarySimulation

Engine

Sys. specificationApp. Requirements

App/task ConstraintsPower management policy

Device driver

Device model

Device broker I

Device status

Device driver

Device model

Device broker II

Device status

Sys/app status