Performance per watt
Encyclopedia
In computing
, performance per watt is a measure of the energy efficiency
of a particular computer architecture
or computer hardware
. Literally, it measures the rate of computation
that can be delivered by a computer for every watt
of power consumed.
The performance and power consumption metrics used depend on the definition; reasonable measures of performance are FLOPS
, MIPS
, or the score for any performance benchmark
. Several measures of power usage may be employed, depending on the purposes of the metric; for example, a metric might only consider the electrical power delivered to a machine directly, while another might include all power necessary to run a computer, such as cooling and monitoring systems. Often the power is the average power used while running the benchmark, but sometimes other measures of power usage may be employed (e.g. peak power, idle power.)
For example, the early UNIVAC I
computer performed approximately 0.015 operations per watt-second (performing 1,905 operations per second, while consuming 125 kW).
Most of the power a computer uses is converted into heat, so a system that takes fewer watts to do a job will require less cooling to maintain a given operating temperature
. Reduced cooling demands makes it easier to quiet a computer
. Lower energy consumption can also make it less costly to run, and reduce the environmental impact of powering the computer (see green computing
).
If installed where there is limited climate control, a lower power computer will operate at a lower temperature, which may make it more reliable. In a climate controlled environment, reductions in direct power use may also create savings in climate control energy.
Computing energy consumption is sometimes also measured by reporting the energy required to run a particular benchmark, for instance EEMBC
EnergyBench. Energy consumption figures for a standard workload may make it easier to judge the effect of an improvement in energy efficiency, just as the use of L/100km is easier than reciprocal measures (such as miles per gallon) when judging impact of automotive fuel economy.
Performance (in operations/second) per watt can also be written as operations/watt-second, or operations/joule, since 1 watt = 1 joule/second.
(Floating Point
Operations Per Second) per watt is a common measure. Like the FLOPS it is based on, the metric is usually applied to scientific computing and simulations involving many floating point calculations.
in terms of FLOPS per Watt, running at 2097.19 MFLOPS/Watt.
On 9 June 2008, CNN reported that IBM's Roadrunner supercomputer achieves 376 MFLOPS/Watt. In November 2010, IBM machine, Blue Gene/Q achieves 1684 MFLOPS/Watt.
As part of Intel's Tera-Scale
research project, the team produced an 80 core CPU that can achieve over 16 GFLOPS/Watt.
The future of that CPU is not certain.
Microwulf, a low cost desktop Beowulf cluster
of 4 dual core Athlon 64 x2 3800+ computers, runs at 58 MFLOPS/Watt.
list of supercomputers in terms of energy efficiency. Typically measured as LINPACK
FLOPS per watt.
s (GPU) have continued to increase in energy usage, while CPUs designers have recently focused on improving performance per watt. High performance GPUs may now be the largest power consumer in a system. Measures like 3DMark2006 score
per watt can help identify more efficient GPUs. However that may not adequately incorporate efficiency in typical use, where much time is spent doing less demanding tasks.
With modern GPUs, energy usage is an important constraint on the possible power. GPU designs are usually highly scalable, allowing the manufacturer to put multiple chips on the same video card, or to use multiple video cards that work in parallel. Peak performance of any system is essentially limited by the amount of power it can draw and the amount of heat it can dissipate. Consequently, performance per watt of a GPU design translates directly into peak performance of a system that uses that design.
Since GPUs may also be used for some general purpose computation
, sometimes their performance is measured in terms also applied to CPUs, such as FLOPS per watt.
Benchmarks that measure power under heavy load may not adequately reflect typical efficiency. For instance, 3DMark stresses the 3D performance of a GPU, but many computers spend most of their time doing less intense display tasks (idle, 2D tasks, displaying video). So the 2D or idle efficiency of the graphics system may be at least as significant for overall energy efficiency. Likewise, systems that spend much of their time in standby or soft off
are not adequately characterized by just efficiency under load. To help address this some benchmarks, like SPECpower
, include measurements at a series of load levels.
The efficiency of some electrical components, such as voltage regulators
, decreases with increasing temperature, so the power used may increase with temperature. Power supplies, motherboards, and some video cards are some of the subsystems affected by this. So their power draw may depend on temperature, and the temperature or temperature dependence should be noted when measuring.
Performance per watt also typically does not include full life-cycle costs
. Since computer manufacturing is energy intensive, and computers often have a relatively short lifespan, energy and materials involved in production, distribution, disposal
and recycling
often make up significant portions of their cost, energy use, and environmental impact.
Energy required for climate control of the computer's surroundings is often not counted in the wattage calculation, but can be significant.
metric for data centers, incorporating energy and space.
SWaP = Performance/(Space x Power)
Where performance is measured by any appropriate benchmark, and space is size of the computer.
Other:
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, performance per watt is a measure of the energy efficiency
Energy conversion efficiency
Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat.-Overview:...
of a particular computer architecture
Computer architecture
In computer science and engineering, computer architecture is the practical art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals and the formal modelling of those systems....
or computer hardware
Computer hardware
Personal computer hardware are component devices which are typically installed into or peripheral to a computer case to create a personal computer upon which system software is installed including a firmware interface such as a BIOS and an operating system which supports application software that...
. Literally, it measures the rate of computation
Computer performance
Computer performance is characterized by the amount of useful work accomplished by a computer system compared to the time and resources used.Depending on the context, good computer performance may involve one or more of the following:...
that can be delivered by a computer for every watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
of power consumed.
The performance and power consumption metrics used depend on the definition; reasonable measures of performance are FLOPS
FLOPS
In computing, FLOPS is a measure of a computer's performance, especially in fields of scientific calculations that make heavy use of floating-point calculations, similar to the older, simpler, instructions per second...
, MIPS
Instructions per second
Instructions per second is a measure of a computer's processor speed. Many reported IPS values have represented "peak" execution rates on artificial instruction sequences with few branches, whereas realistic workloads typically lead to significantly lower IPS values...
, or the score for any performance benchmark
Benchmark (computing)
In computing, a benchmark is the act of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it...
. Several measures of power usage may be employed, depending on the purposes of the metric; for example, a metric might only consider the electrical power delivered to a machine directly, while another might include all power necessary to run a computer, such as cooling and monitoring systems. Often the power is the average power used while running the benchmark, but sometimes other measures of power usage may be employed (e.g. peak power, idle power.)
For example, the early UNIVAC I
UNIVAC I
The UNIVAC I was the first commercial computer produced in the United States. It was designed principally by J. Presper Eckert and John Mauchly, the inventors of the ENIAC...
computer performed approximately 0.015 operations per watt-second (performing 1,905 operations per second, while consuming 125 kW).
Most of the power a computer uses is converted into heat, so a system that takes fewer watts to do a job will require less cooling to maintain a given operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
. Reduced cooling demands makes it easier to quiet a computer
Quiet PC
A quiet PC is a personal computer that makes little noise. Common uses for quiet PCs include video editing, sound mixing, home servers, and home theater PCs. A typical quiet PC uses quiet cooling and storage devices and energy-efficient parts....
. Lower energy consumption can also make it less costly to run, and reduce the environmental impact of powering the computer (see green computing
Green computing
Green computing or green IT, refers to environmentally sustainable computing or IT. In the article Harnessing Green IT: Principles and Practices, San Murugesan defines the field of green computing as "the study and practice of designing, manufacturing, using, and disposing of computers, servers,...
).
If installed where there is limited climate control, a lower power computer will operate at a lower temperature, which may make it more reliable. In a climate controlled environment, reductions in direct power use may also create savings in climate control energy.
Computing energy consumption is sometimes also measured by reporting the energy required to run a particular benchmark, for instance EEMBC
EEMBC
EEMBC, the Embedded Microprocessor Benchmark Consortium, is a non-profit organization formed in 1997 with the aim of developing meaningful performance benchmarks for the hardware and software used in embedded systems...
EnergyBench. Energy consumption figures for a standard workload may make it easier to judge the effect of an improvement in energy efficiency, just as the use of L/100km is easier than reciprocal measures (such as miles per gallon) when judging impact of automotive fuel economy.
Performance (in operations/second) per watt can also be written as operations/watt-second, or operations/joule, since 1 watt = 1 joule/second.
FLOPS per watt
FLOPSFLOPS
In computing, FLOPS is a measure of a computer's performance, especially in fields of scientific calculations that make heavy use of floating-point calculations, similar to the older, simpler, instructions per second...
(Floating Point
Floating point
In computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...
Operations Per Second) per watt is a common measure. Like the FLOPS it is based on, the metric is usually applied to scientific computing and simulations involving many floating point calculations.
Examples
, the Green500 list rates IBM NNSA/SC Blue Gene/Q Prototype 2 as the most efficient supercomputer on the TOP500TOP500
The TOP500 project ranks and details the 500 most powerful known computer systems in the world. The project was started in 1993 and publishes an updated list of the supercomputers twice a year...
in terms of FLOPS per Watt, running at 2097.19 MFLOPS/Watt.
On 9 June 2008, CNN reported that IBM's Roadrunner supercomputer achieves 376 MFLOPS/Watt. In November 2010, IBM machine, Blue Gene/Q achieves 1684 MFLOPS/Watt.
As part of Intel's Tera-Scale
Intel Tera-Scale
Intel Tera-scale Computing is a research and development program aiming at scaling Intel multi core architectures for the future.It has so far developed:* 2007: Teraflops Research Chip, an 80 cores processor prototype....
research project, the team produced an 80 core CPU that can achieve over 16 GFLOPS/Watt.
The future of that CPU is not certain.
Microwulf, a low cost desktop Beowulf cluster
Beowulf (computing)
A Beowulf cluster is a computer cluster of what are normally identical, commodity-grade computers networked into a small local area network with libraries and programs installed which allow processing to be shared among them...
of 4 dual core Athlon 64 x2 3800+ computers, runs at 58 MFLOPS/Watt.
Green500 List
The Green500 list ranks computers from the TOP500TOP500
The TOP500 project ranks and details the 500 most powerful known computer systems in the world. The project was started in 1993 and publishes an updated list of the supercomputers twice a year...
list of supercomputers in terms of energy efficiency. Typically measured as LINPACK
LINPACK
LINPACK is a software library for performing numerical linear algebra on digital computers. It was written in Fortran by Jack Dongarra, Jim Bunch, Cleve Moler, and Gilbert Stewart, and was intended for use on supercomputers in the 1970s and early 1980s...
FLOPS per watt.
GPU efficiency
Graphics processing unitGraphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
s (GPU) have continued to increase in energy usage, while CPUs designers have recently focused on improving performance per watt. High performance GPUs may now be the largest power consumer in a system. Measures like 3DMark2006 score
3DMark
3DMark is a computer benchmarking tool created and developed by Futuremark Corporation to determine the performance of a computer's 3D graphic rendering and CPU workload processing capabilities. Running 3DMark produces a 3DMark score with higher numbers indicating better performance...
per watt can help identify more efficient GPUs. However that may not adequately incorporate efficiency in typical use, where much time is spent doing less demanding tasks.
With modern GPUs, energy usage is an important constraint on the possible power. GPU designs are usually highly scalable, allowing the manufacturer to put multiple chips on the same video card, or to use multiple video cards that work in parallel. Peak performance of any system is essentially limited by the amount of power it can draw and the amount of heat it can dissipate. Consequently, performance per watt of a GPU design translates directly into peak performance of a system that uses that design.
Since GPUs may also be used for some general purpose computation
GPGPU
General-purpose computing on graphics processing units is the technique of using a GPU, which typically handles computation only for computer graphics, to perform computation in applications traditionally handled by the CPU...
, sometimes their performance is measured in terms also applied to CPUs, such as FLOPS per watt.
Challenges
While performance per watt is useful, absolute power requirements are also important. Claims of improved performance per watt may be used to mask increasing power demands. For instance, though newer generation GPU architectures may provide better performance per watt, continued performance increases can negate the gains in efficiency, and the GPUs continue to consume large amounts of power..Benchmarks that measure power under heavy load may not adequately reflect typical efficiency. For instance, 3DMark stresses the 3D performance of a GPU, but many computers spend most of their time doing less intense display tasks (idle, 2D tasks, displaying video). So the 2D or idle efficiency of the graphics system may be at least as significant for overall energy efficiency. Likewise, systems that spend much of their time in standby or soft off
Standby power
Standby power, also called vampire power, vampire draw, phantom load, or leaking electricity , refers to the electric power consumed by electronic and electrical appliances while they are switched off Standby power, also called vampire power, vampire draw, phantom load, or leaking electricity...
are not adequately characterized by just efficiency under load. To help address this some benchmarks, like SPECpower
SPECpower
SPECpower_ssj2008 is the first industry-standard benchmark that evaluates the power and performance characteristics of volume server class computers. It is available from the Standard Performance Evaluation Corporation . SPECpower_ssj2008 is SPEC's first attempt at defining server power measurement...
, include measurements at a series of load levels.
The efficiency of some electrical components, such as voltage regulators
Voltage regulator
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components...
, decreases with increasing temperature, so the power used may increase with temperature. Power supplies, motherboards, and some video cards are some of the subsystems affected by this. So their power draw may depend on temperature, and the temperature or temperature dependence should be noted when measuring.
Performance per watt also typically does not include full life-cycle costs
Life cycle assessment
A life-cycle assessment is a technique to assess environmental impacts associated with all the stages of a product's life from-cradle-to-grave A life-cycle assessment (LCA, also known as life-cycle analysis, ecobalance, and cradle-to-grave analysis) is a technique to assess environmental impacts...
. Since computer manufacturing is energy intensive, and computers often have a relatively short lifespan, energy and materials involved in production, distribution, disposal
Electronic waste
Electronic waste, e-waste, e-scrap, or Waste Electrical and Electronic Equipment describes discarded electrical or electronic devices. There is a lack of consensus as to whether the term should apply to resale, reuse, and refurbishing industries, or only to product that cannot be used for its...
and recycling
Computer recycling
Computer recycling or electronic recycling is the recycling or reuse of computers or other electronics. It includes both finding another use for materials , and having systems dismantled in a manner that allows for the safe extraction of the constituent materials for reuse in other...
often make up significant portions of their cost, energy use, and environmental impact.
Energy required for climate control of the computer's surroundings is often not counted in the wattage calculation, but can be significant.
Other energy efficiency measures
SWaP (space, wattage and performance) is a Sun MicrosystemsSun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
metric for data centers, incorporating energy and space.
SWaP = Performance/(Space x Power)
Where performance is measured by any appropriate benchmark, and space is size of the computer.
See also
Energy efficiency benchmarks:- Average CPU PowerAverage CPU PowerThe average CPU power , is a scheme to characterize power consumption of new central processing units under "average" daily usage, especially server processors, the rating scheme is defined by Advanced Micro Devices for use in its line of processors based on the K10 microarchitecture...
Measures power used running several standard benchmarks. - SPECpowerSPECpowerSPECpower_ssj2008 is the first industry-standard benchmark that evaluates the power and performance characteristics of volume server class computers. It is available from the Standard Performance Evaluation Corporation . SPECpower_ssj2008 is SPEC's first attempt at defining server power measurement...
Benchmark for web servers running Java. (Server Side Java Operations per Joule) - EEMBCEEMBCEEMBC, the Embedded Microprocessor Benchmark Consortium, is a non-profit organization formed in 1997 with the aim of developing meaningful performance benchmarks for the hardware and software used in embedded systems...
EnergyBench.
Other:
- GeForce 9 SeriesGeForce 9 SeriesThe GeForce 9 Series is the ninth generation of NVIDIA's GeForce series of graphics processing units, the first of which was released on February 21, 2008.-Geforce 9300GE :*65nm G98 GPU*PCI-E x16*64 Bit Bus Width*4 ROP, 8 Unified Shaders...
GPU list, has energy use and theoretical FLOPS. - Power usage effectivenessPower usage effectivenessPower usage effectiveness is a measure of how efficiently a computer data center uses its power; specifically, how much of the power is actually used by the computing equipment ....
(PUE) - Data center infrastructure efficiencyData center infrastructure efficiencyData center infrastructure efficiency , is a performance improvement metric used to calculate the energy efficiency of a data center...
(DCIE) - low-power electronicsLow-power electronicsLow-power electronics means that the consumption of electric power is deliberately low, e.g. notebook processors.- Computing elements :The density and speed of integrated-circuit computing elements have increased exponentially for several decades, following a trend described by Moore's Law...
- IT energy managementIT energy managementIT energy management is the analysis and management of energy demand within the information technology arena. IT energy demand accounts for approximately 2% of global CO2 emissions, approximately the same level as aviation...