DepartmentofInforma-onTechnology,UppsalaUniversity h9p://it.uu.se/

UARTUppsalaArchitecture

ResearchTeam

HowCanWeImproveDAE?

DAE=DecouplingUsesfromLoads

Selec-ngLoads:Crea-ngAlterna-veAccessPhases

WhyDAE?DAE+FrequencyScalingSavesEnergy

Evalua-ngVersionsatRun-meandSelec-ngtheBestPerformingOne

OvercomingAddressRecomputa-on:Hois-ngLoadstoAccessPhases Info

Problem:Hois-ngallloadsIntoanAccessPhaseIsinfeasible:addresscomputa-onoverheaddiminishesbenefits!

So)wareDecoupledAccess-ExecuteKim-AnhTran,Konstan-nosKoukos,StefanosKaxiras,AlexandraJimborean

Whichloadstoselectforprefetching?

Howtoavoidaddress

recomputa-on?

1

2

1

2

Run>meEvalua>onPhase:evaluateeachcombina-on!

Pickbestcombina-onforremainingitera-ons

A0 E E EA1 EA1 EA1A1 A2 EOrig ...

Run-t

ime

Iteration0 10 20 30 40 50 60slice 0 slice 1 slice 2 slice 3 slice 4 slice 5 ...Loop

Slice

Original

DAE

CPUfrequency fopt

CPUfrequencyfmax

fminExecu�on

Memory-bound:runon lowfrequency

Compute-bound:runonhighfrequency

Originalcode:compromisefrequencytobalancebetweenenergyandperformance.

DAEhelpstosaveenergybyadjus�ngthefrequency.

vs.

Problem:Addressrecomputa3onintheExecutePhaseisexpensive.

CreateoneAccessPhaseforeachlevelofindirec-on:

Orig OriginalCode

Legend

n-thAccessVersion

ExecutePhase(sameforallAn)

An

E

Runeachversion(Originalandalterna-veAccess-Executeversions)foracoupleofitera>ons

wasiden-fiedasthebestperformingversion:se9leonthiscombina-on!

for(...){

}

unroll*2L1=ldx[i]L2=ldy[i]L1+L2

for(...){in-placeDAE

L1=ldx[i]L2=ldy[i]L1+L2

}

L3=ldx[i+1]L4=ldy[i+1]L3+L4

for(...){

L1=ldx[i]L2=ldy[i]

L1+L2

}

L3=ldx[i+1]L4=ldy[i+1]

L3+L4

Register

TransferofdatafromAccesstoExecute

viaregisters

AccessPhase

ExecutePhase

for(...){

}

for (...) {

x[i]

for (...) { for (...) {

Version1:1-indirec�on

a[x[i]]b[a[x[i]]]

y[i]

Indirec�on

Legend

AccessPhase

ExecutePhase

or or

Version2:2-indirec�on

Version3:3-indirec�on

x[i]y[i]

x[i]a[x[i]]

y[i]

}

x[i]a[x[i]]

y[i]

x[i]a[x[i]]

b[a[x[i]]]y[i]

} }for (...) {

}

for (...) {

}

for (...) {

}

for(...){

}

for(...){

}

AccessPhase

ExecutePhase

MemoryAccessComputa�on

Cache

prefetchintocache

usedata

for(...){

}Legend

WhyDAEwithinoneloop?ByapplyingDAEwithinoneloop,wemaytransferdataviaregisters:Accessphaseloadsdataintoaregister,Executephasedirectlyuses

register.

Whyunrolling?UnrollingisrequiredaswenowapplyDAEwithintheloop

Reference:A.Jimborean,K.Koukos,V.Spiliopoulos,D.Black-Schaffer,S.Kaxiras.Fixthecode.Don’ttweakthehardware:AnewcompilerapproachtoVoltage-Frequencyscaling.InProc.ofCGO’14

Contact:kim-anh.tran@it.uu.se