Download - Energy Efficient Programming - uni-hamburg.de...Motivation Hardwarelayer OSlayer Applicationlayer Conclusion Literature DVFS DVFS Dynamic Frequency and Voltage Scaling P static = m

Motivation Hardware layer OS layer Application layer Conclusion Literature

Energy Efficient Programming

Merlin Steuer

Seminar Effiziente ProgrammierungArbeitsbereich Wissenschaftliches Rechnen

Fachbereich InformatikFakultät für Mathematik, Informatik und Naturwissenschaften

Universität Hamburg

24.11.2016

Merlin Steuer Energy Efficient Programming 1 / 42


Outline

1 Motivation

2 Energy saving at hardware layer

3 Energy saving at OS layer

4 Energy saving at application layer

5 Conclusion

6 Literature



Motivation



Motivation

Power Consumption IS a deal nowadaysDKRZ: ∼ 1,2 MW⇒∼ 10,5 GWh/yr1!∼ 2800 households (3 persons)2

1[1]2[2]



More power...

Top500 No. 2: National Super Computer Center in Guangzhou∼ 18 MW 3

∼ 160 GWh/yr∼ 41000 households 4

10x Reinfeld (Holst.)! 5

3[1]4[2]5[3], [4]



Hardware layer



Overview

Overview

DVFS - Dynamic voltage and frequency scalingACPI - Advanced Configuration and Power Interface



DVFS

DVFS

Dynamic Frequency and Voltage Scaling

Pstatic = m · V 1

m = const.V : Core voltage

P = 12C · V 2 · f + Pstatic

6

C : capacitance of switched circuitV : Voltage of switched circuitf : Frequency

6[5]Merlin Steuer Energy Efficient Programming 8 / 42


DVFS

DVFS

Dynamic Frequency and Voltage ScalingPstatic = m · V 1

m = const.V : Core voltage

P = 12C · V 2 · f + Pstatic

6

C : capacitance of switched circuitV : Voltage of switched circuitf : Frequency



DVFS

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100% P

ow

er

Consu

mpti

on (

of

10

0%

Core

Volt

age)

% Core Voltage

Power consumption by core voltage

Power

Figure: Power vs. Voltage

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100% P

ow

er

Consu

mpti

on (

of

10

0%

Core

Volt

age)

% Core Frequency

Power consumption by core frequency

Power

Figure: Power vs. Frequency



DVFS

DVFS

Possible f is a function of VLower f ⇒ Lower execution speedGood for memory-intensive applicationsNot useful for CPU-intensive applicationsCareful! Sometimes f ↘ ⇒Memory Bandwith ↘ 7



ACPI

ACPI

Advanced Configuration and Power InterfaceIndustrial standardAllows OS-directed control over voltage and frequency of asystemP(erformance)-States and C(ore)-States



ACPI

P-States

P0: Normal operation, highest performance and powerconsumptionPi , i > 0: Reduced power consumption, reduced performanceExample: AMD Opteron 6128 @ 2.0 GHz 8

i Vi (V) fi (GHz)0 1.23 2.001 1.17 1.502 1.12 1.203 1.09 1.004 1.06 0.80



ACPI

C-States

Core statesCannot be set by code, only by hardware⇒Conditions can be set, so the hardware sets a specificC-StateC0: Normal operationCi , i > 0: Core halted, transition time to C0 rises with higher iCan be set on core or socket level, depending on CPU



ACPI

C-States

Figure: Different C-States (example)9



OS layer



Overview

Overview

The OS manages all peripherals within a computer system⇒Can have a large impact on power consumptionCan switch different peripherals within the CPU to reduce Cin P = 1

2C · V 2 · f



Overview

Peripherals

Peripheral Power consumption (Watt) 10

CPU 102 - 103Graphics Card 102 - 103

HDD ∼ 10 eachOptical Drives ∼ 10

Network Interfaces ∼ 10RAM ∼ 3 - 5 per module

Mainboard 25 - 40



Saving energy within the OS

Energy efficient OS

Graphics cardUse lower voltage / frequencyIf present: use second low-power graphics card

HDDReduce load to HDD by cachingUse differend Power-(Spindown-)States if disc is idle

Network interfacesUse lower speeds ⇒ switch to 100MBit connection if 1GBitconnection is not needed



Saving energy within the OS

Energy efficient OS

CPUImproved SchedulingEnter higher P-States or even C-States when CPU is idle

Memory: Efficient layoutRAM accesses need energyGood memory layout allows better caching ⇒ less read-accesses

Mainboard peripherals can be disabled if unused to save power



Application layer



Overview

Overview

We need to know what happens under the hoodHave energy efficiency in mind when writing programsGenerally: Time-efficient programs are often energy efficient



Energy-aware programming techniques

Techniques

Increasing time efficiencyIncreasing data efficiencyLetting the CPU restChoosing a languageLetting the compiler help usLibraries




Time efficiency

Many problems may be solved fast than the trivial approachExample: Bubblesort vs. QuicksortO(n2) vs. O(n log n) (Average case)Sort a list with 106 entries

1012 vs. 6 · 106 steps




Algorithms

Another example: Sub-String searchingTrivial aproach: O(n ·m)Boyer-Moore: O(n + m)

Algorithms allowing the CPU to Idle are betterRecursive algorithms are nice, but usually energy-inefficient(Cache misses)




Data efficiency

Data efficiency causes less memory operations ⇒more energyefficientMore cache hits ⇒ less execution timeTime efficiency vs. Data efficiencyChoose your data structures wisely!




Example: Lists11

Linked List vs. ArrayLinked lists (SE I) seem great, but:

Read in O( n2 ) vs. O(1)

Each container-object is located at different memory locations⇒Cache miss for nearly every step

Use linked lists only if you append a lot and have no need tooften traverse the whole listImagine a bubble sort in a linked list with 106 entries




Logging12

Logging is great during developementLogging to the hard disc is causing the drive to spin up veryoftenReduce logging to the minimum needed, maintaining theinformationCache messages




Letting the CPU rest

A sleeping CPU is a good CPUExample: Network communications




Example13: Network communication: Don’t

1 while (true)2 {3 // Read data4 result = recv( serverSocket , buffer , bufferLen , 0);56 // Handle data7 if( result != 0)8 {9 HandleData ( buffer );

10 }1112 // Sleep and repeat13 Sleep (1000) ;14 }




Example: Network communication: Do

1 WSANETWORKEVENTS NetworkEvents ;2 WSAEVENT wsaSocketEvent ;3 wsaSocketEvent = WSACreateEvent ();4 WSAEventSelect ( serverSocket , wsaSocketEvent ,

↪→ FD_READ | FD_CLOSE );5 while (true)6 {7 // Wait until data will be available in the socket8 WaitForSingleObject ( wsaSocketEvent , INFINITE );9 // Read data

10 result = recv( serverSocket , buffer , bufferLen , 0);1112 // Handle data13 if( result != 0)14 {15 HandleData ( buffer );16 }17 }Merlin Steuer Energy Efficient Programming 30 / 42



When talking about communication14

Network communication needs energyKeep your protocols slimreduce overhead to a minimumSend big messages less frequent than small ones very often⇒ less CPU-wake-ups



Considerations

Choosing a language15

Lower level languages like C, C++ are better for energyefficiencyMore control over memory and program flowHigh-Level languages (C#, Java) are convenient, but coder hasless controlPrefer compiled languages over interpreted ones



Considerations

Letting the compiler help us16

If possible, let the compiler use architecture-specific instructionsetsHardware acceleration gives a huge boost in efficiencyLet the compiler optimize the code (-Ox)Less instructions per task ⇒ better efficiency



Considerations

Libraries

A Lot of tasks have been solved alreadyLibraries save time and moneyMultithreading/Parallel computing may give a goodperformance improvement:

OpenMPMPI

Search for Libraries before inventing the wheel over and overagain



Conclusion



Conclusion

To make a program energy-efficient, it’s good to know whathappens in hardwareKnow what the OS does to make a system energy efficientSimple rules make programs more efficientThink about your problem - The trivial approach is the best inrare cases only



Thank you.Questions?



Literature



Literature I

[1] Top500.org. Top500 list november 2016. Accessed: 15.11.2016.[Online]. Available: https://www.top500.org/list/2016/11/

[2] Die-Stromsparinitiative.de. Stromverbrauch im haushalt:Durchschnitt und spartipps. Accessed: 15.11.2016. [Online].Available: http://www.die-stromsparinitiative.de/stromkosten/stromverbrauch-pro-haushalt/

[3] B. für politische Bildung. Bevölkerung und haushalte. Accessed:15.11.2016. [Online]. Available:http://www.bpb.de/nachschlagen/zahlen-und-fakten/soziale-situation-in-deutschland/61584/bevoelkerung-und-haushalte


https://www.top500.org/list/2016/11/

http://www.die-stromsparinitiative.de/stromkosten/stromverbrauch-pro-haushalt/

http://www.die-stromsparinitiative.de/stromkosten/stromverbrauch-pro-haushalt/

http://www.bpb.de/nachschlagen/zahlen-und-fakten/soziale-situation-in-deutschland/61584/bevoelkerung-und-haushalte




Literature II

[4] Reinfeld.de. Starting page. Accessed: 15.11.2016. [Online].Available: http://www.reinfeld.de/

[5] M. Travers, “CPU Power Consumption Experiments andResults Analysis of Intel i7-4820K,” p. 5, 2015. [Online].Available: http://async.org.uk/tech-reports/NCL-EEE-MICRO-TR-2015-197.pdf

[6] D. M. Robert Schone, Daniel Hackenberg, “Memoryperformance at reduced cpu clock speeds: An analysis ofcurrent x86 64 processors,” p. 3, 2014. [Online]. Available:https://pdfs.semanticscholar.org/8668/5044b78aed871688f4c7e8d95b4b62538570.pdf


http://www.reinfeld.de/

http://async.org.uk/tech-reports/NCL-EEE-MICRO-TR-2015-197.pdf

http://async.org.uk/tech-reports/NCL-EEE-MICRO-TR-2015-197.pdf

https://pdfs.semanticscholar.org/8668/5044b78aed871688f4c7e8d95b4b62538570.pdf

https://pdfs.semanticscholar.org/8668/5044b78aed871688f4c7e8d95b4b62538570.pdf


Literature III

[7] M. Dolz, “Paving the way towards energy-awarehigh-performance-computing,” p. 18, 2014. [Online]. Available:https://wr.informatik.uni-hamburg.de/_media/teaching/wintersemester_2014_2015/eep-1415-eehpc.pdf

[8] Cprogramming. Green code developement. Accessed:15.11.2016. [Online]. Available:http://www.cprogramming.com/appup6.html

[9] buildcomputers. Power consumption of pc components inwatts. Accessed: 15.11.2016. [Online]. Available:http://www.buildcomputers.net/power-consumption-of-pc-components.html


https://wr.informatik.uni-hamburg.de/_media/teaching/wintersemester_2014_2015/eep-1415-eehpc.pdf

https://wr.informatik.uni-hamburg.de/_media/teaching/wintersemester_2014_2015/eep-1415-eehpc.pdf

http://www.cprogramming.com/appup6.html

http://www.buildcomputers.net/power-consumption-of-pc-components.html

http://www.buildcomputers.net/power-consumption-of-pc-components.html


Literature IV

[10] D. Lohmann, “Energy-aware programming techniques,” 2014.[Online]. Available: https://wr.informatik.uni-hamburg.de/_media/teaching/wintersemester_2014_2015/eep-1415-lohmann-programming-techniques.pdf

[11] C. Weekly. 8 ways to make your software applications moreenergy efficient. Accessed: 15.11.2016. [Online]. Available:http://www.computerweekly.com/blog/Green-Tech/8-ways-to-make-your-software-applications-more-energy-efficient


https://wr.informatik.uni-hamburg.de/_media/teaching/wintersemester_2014_2015/eep-1415-lohmann-programming-techniques.pdf



http://www.computerweekly.com/blog/Green-Tech/8-ways-to-make-your-software-applications-more-energy-efficient

http://www.computerweekly.com/blog/Green-Tech/8-ways-to-make-your-software-applications-more-energy-efficient