Types for Energy Management

Yu David Liu

State University of New York (SUNY)

at Binghamton

OOPSLA’13 PC Workshop

2

Energy Efficiency in Computing

PL & SEefforts

PACT, ASPLOS

OSDI, SOSP, SenSys,

SIGCOMMISCA,

MICRO, HPCA

VLSI, DAC

operational cost phone battery

life sensor network

usability system

reliability (overheating)

environment

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High-Level Questions

What are the principles of energy management? recurring themes of software-hardware

interactions recurring themes of static-dynamic interactions

How can the principles be abided by at software construction time (or through software lifecycle)?

What is the role of programmers in energy-efficient computing?

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This Talk

An energy-aware programming language design

Core Idea: building the principles of energy management into a type system Static Typing:

Michael Cohen, Haitao Steve Zhu, Senem Ezgi Emgin, Yu David Liu, "Energy Types," OOPSLA’12.

Hybrid Typing: ongoing work

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Energy Types

Phase• A pattern of system (CPU, memory…) utilization• “math”, “graphics”, “audio”…

• A level of energy state• “battery low”, “battery high”, “battery charged”…

Mode

A type system to reason about energy management based on

two concepts:

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Energy Types

Phase• A pattern of system (CPU, memory…) utilization• “math”, “graphics”, “audio”…

• A level of energy state• “battery low”, “battery high”, “battery charged”

Mode

A type system to reason about energy management based on

two concepts:

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CPU-boundclass Compute{

…

void doCompute(){

for(int i = 0; i < N; i++){

pi += factor/(2 * i + 1);

factor /= -3.0;

}}}

class Draw{

…

void doDraw(){

for(int i = 0; i < NUM; i++) {

canvas.drawL(x[i], y[i],);

c.draw(getImg(), rect);

}}}

I/O-bound

Phases in Programs

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Draw draw = new Draw();

Compute cmpt = new Compute();

draw.doDraw();

cmpt.doCompute();

Draw draw = new Draw();

Phases in Programs

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Draw draw = new Draw();

Compute@phase(math) cmpt = new Compute();

draw.doDraw();

cmpt.doCompute();

Draw@phase(graphics) draw = new Draw();

phases { graphics <cpu math}

Phases as Type Qualifiers

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DVFS in Energy Management

Energy = Power * Time

Dynamic Voltage & Frequency Scaling (DVFS)

Power = c * Frequency * V2

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Phase-based Energy Management

What: divide execution into distinct system utilization “phases”, and scale down CPU frequency when a phase is not CPU-bound

Why: minimum performance degradation with maximum energy savings

Energy Types Solution: use (declared or inferred) phase types to guide DVFS

A case of software-hardware interaction for energy management

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Draw draw = new Draw();

Compute@phase(math) cmpt = new Compute();

draw.doDraw();

cmpt.doCompute();

Draw@phase(graphics) draw = new Draw();

phases { graphics <cpu math}

Phases as Type Qualifiers

CPU frequency scaled through

compiler instrumentation

CPU frequency scaled through

compiler instrumentation

Energy Management through Type-Directed DVFS:

1. tap programmer knowledge 2. tap type systems’ ability for consistency checking, type propagation and inference

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Invariants Phase distinction: No object can

commit to more than one phase Phase isolation: an object can only

send messages to an object belonging to the same phase Inter-phase messaging is only

allowed through explicit type coercion

Promoting phased behaviors

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Type System DetailsBased on region types: phases are

regionsParametric polymorphism:

Different objects of the same class can have different phases

Finer-grained support through method polymorphism

Explicit form: “generic” phases Implicit form: polymorphic inference

to allow for arbitrary qualifier elisionType Soundness

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Energy Types

Phase• A pattern of CPU and memory utilization• “math”, “graphics”, “audio”

• A level of energy state expectation• “battery low”, “battery high”, “battery charged”

Mode

A type system to reason about energy management based on

two concepts

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Renderer m1 = new Renderer(0.99);Renderer m2 = new Renderer(0.5);

Objects of different qualities

Mode-based Energy Managementclass Renderer{ Renderer(double quality){ int loopNum = 1000 * quality; for(int i = 0; i < loopNum; i++){ render(canvas, i); }}}

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Renderer m1 = new Renderer(0.99);

Renderer m2 = new Renderer(0.5);

Modes as Type Qualifiers

modes { low <: hi; }

Renderer@mode(hi) m1 = new Renderer(0.99);

Renderer@mode(low) m2 = new Renderer(0.5);

Encouraging Application-Specific Energy Savings

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Invariants waterfall Invariant: an object can

only send messages to an object of the same mode, or of a “lower” mode in the partial order A program in “high” energy state can

invoke code supposed to be used in “low” energy state

The other way around requires explicit type coercion

Regulating Energy States

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Type System DetailsBased on region types: modes are

regionsParametric polymorphism:

Different objects of the same class can have different modes

Finer-grained support through method polymorphism

Explicit form: “generic” modes Implicit form: polymorphic inference

to allow for arbitrary qualifier elisionType Soundness

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Ongoing Effort: Hybrid Typingclass Network { void send() {…}}

class Client {…Network n = new Network();while (…) { n.send();}}

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Ongoing Effort: Hybrid Typingclass Network { void send() {…}}

class Client {…Network@mode(hi) n = new Network();while (…) { n.send();}}

Hmm..

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Ongoing Effort: Hybrid Typingclass Network { void send() {…}}

class Client {…Network@mode(low) n = new Network();while (…) { n.send();}}

Hmm..

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Dynamic Typesclass Network { void send() {…}}

class Client {…Network@mode(dynamic) n = new Network();while (…) { n.send();}}

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From Dynamic to Static (One Possible Design)

class Network { void send() {…}}

class Client {…Network@mode(dynamic) n = new Network();while (…) { ((Network@mode(low))n).send();}}

Client MakesDecision

Hmm..

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From Dynamic to Static (Our Design)class Network { void send() {…} ~ Network () { if (…) return hi else return low; }}

class Client {…Network@mode(dynamic) n = new Network();while (…) { attribute n to low { n.send(); }}}

Bi-DirectionalDecision

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Implementation and Evaluation

Prototyped compiler for Android Apps

Static typing: benchmarking results show promising energy savings with minimal performance loss For some game benchmarks, 40%

energy savings and 2% performance loss with phases; application-specific with modes

Hybrid typing: under development

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Conclusions

New language designs may capture and facilitate complex software/hardware static/dynamic interactions in energy management

Principles of energy management may be enforced by type systems

Energy-aware programming broadens the scope of energy optimization by bringing in programmer knowledge

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Q&A