Power management

Last updated

Power management is a feature of some electrical appliances, especially copiers, computers, computer CPUs, computer GPUs and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power state when inactive. In computing this is known as PC power management and is built around a standard called ACPI which superseded APM. All recent computers have ACPI support.

Contents

Motivations

PC power management for computer systems is desired for many reasons, particularly:

Lower power consumption also means lower heat dissipation, which increases system stability, and less energy use, which saves money and reduces the impact on the environment.

Processor level techniques

The power management for microprocessors can be done over the whole processor, or in specific components, such as cache memory and main memory.

With dynamic voltage scaling and dynamic frequency scaling, the CPU core voltage, clock rate, or both, can be altered to decrease power consumption at the price of potentially lower performance. This is sometimes done in real time to optimize the power-performance tradeoff.

Examples:

Additionally, processors can selectively power off internal circuitry (power gating). For example:

Intel VRT technology split the chip into a 3.3V I/O section and a 2.9V core section. The lower core voltage reduces power consumption.

Heterogeneous computing

ARM's big.LITTLE architecture can migrate processes between faster "big" cores and more power efficient "LITTLE" cores.

Operating system level: hibernation

When a computer system hibernates it saves the contents of the RAM to disk and powers down the machine. On startup it reloads the data. This allows the system to be completely powered off while in hibernate mode. This requires a file the size of the installed RAM to be placed on the hard disk, potentially using up space even when not in hibernate mode. Hibernate mode is enabled by default in some versions of Windows and can be disabled in order to recover this disk space.

In GPUs

Graphics processing unit (GPUs) are used together with a CPU to accelerate computing in variety of domains revolving around scientific, analytics, engineering, consumer and enterprise applications. [4] All of this comes with some drawbacks, the high computing capability of GPUs comes at the cost of high power dissipation. Much research has been done over the power dissipation issue of GPUs and many techniques have been proposed to address this issue. Dynamic voltage scaling/dynamic frequency scaling (DVFS) and clock gating are two commonly used techniques for reducing dynamic power in GPUs.

DVFS techniques

Experiments show that conventional processor DVFS policy can achieve power reduction of embedded GPUs with reasonable performance degradation. [5] New directions for designing effective DVFS schedulers for heterogeneous systems are also being explored. [6] A heterogeneous CPU-GPU architecture, GreenGPU [7] is presented which employs DVFS in a synchronized way, both for GPU and CPU. GreenGPU is implemented using the CUDA framework on a real physical testbed with Nvidia GeForce GPUs and AMD Phenom II CPUs. Experimentally it is shown that the GreenGPU achieves 21.04% average energy savings and outperforms several well-designed baselines. For the mainstream GPUs which are extensively used in all kinds of commercial and personal applications several DVFS techniques exist and are built into the GPUs alone, AMD PowerTune and AMD ZeroCore Power are the two dynamic frequency scaling technologies for AMD graphic cards. Practical tests showed that reclocking a GeForce GTX 480 can achieve a 28% lower power consumption while only decreasing performance by 1% for a given task. [8]

Power gating techniques

Much research has been done on the dynamic power reduction with the use of DVFS techniques. However, as technology continues to shrink, leakage power will become a dominant factor. [9] Power gating is a commonly used circuit technique to remove leakage by turning off the supply voltage of unused circuits. Power gating incurs energy overhead; therefore, unused circuits need to remain idle long enough to compensate this overheads. A novel micro-architectural technique [10] for run-time power-gating caches of GPUs saves leakage energy. Based on experiments on 16 different GPU workloads, the average energy savings achieved by the proposed technique is 54%. Shaders are the most power hungry component of a GPU, a predictive shader shut down power gating technique [11] achieves up to 46% leakage reduction on shader processors. The Predictive Shader Shutdown technique exploits workload variation across frames to eliminate leakage in shader clusters. Another technique called Deferred Geometry Pipeline seeks to minimize leakage in fixed-function geometry units by utilizing an imbalance between geometry and fragment computation across batches which removes up to 57% of the leakage in the fixed-function geometry units. A simple time-out power gating method can be applied to non-shader execution units which eliminates 83.3% of the leakage in non-shader execution units on average. All the three techniques stated above incur negligible performance degradation, less than 1%. [12]

See also

Related Research Articles

<span class="mw-page-title-main">Overclocking</span> Practice of increasing the clock rate of a computer to exceed that certified by the manufacturer

In computing, overclocking is the practice of increasing the clock rate of a computer to exceed that certified by the manufacturer. Commonly, operating voltage is also increased to maintain a component's operational stability at accelerated speeds. Semiconductor devices operated at higher frequencies and voltages increase power consumption and heat. An overclocked device may be unreliable or fail completely if the additional heat load is not removed or power delivery components cannot meet increased power demands. Many device warranties state that overclocking or over-specification voids any warranty, but some manufacturers allow overclocking as long as it is done (relatively) safely.

<span class="mw-page-title-main">Processor power dissipation</span> Production of waste heat by computer processors

Processor power dissipation or processing unit power dissipation is the process in which computer processors consume electrical energy, and dissipate this energy in the form of heat due to the resistance in the electronic circuits.

Underclocking, also known as downclocking, is modifying a computer or electronic circuit's timing settings to run at a lower clock rate than is specified. Underclocking is used to reduce a computer's power consumption, increase battery life, reduce heat emission, and it may also increase the system's stability, lifespan/reliability and compatibility. Underclocking may be implemented by the factory, but many computers and components may be underclocked by the end user.

<span class="mw-page-title-main">Graphics processing unit</span> Specialized electronic circuit; graphics accelerator

A graphics processing unit (GPU) is a specialized electronic circuit initially designed to accelerate computer graphics and image processing. After their initial design, GPUs were found to be useful for non-graphic calculations involving embarrassingly parallel problems due to their parallel structure. Other non-graphical uses include the training of neural networks and cryptocurrency mining.

AMD Cool'n'Quiet is a CPU dynamic frequency scaling and power saving technology introduced by AMD with its Athlon XP processor line. It works by reducing the processor's clock rate and voltage when the processor is idle. The aim of this technology is to reduce overall power consumption and lower heat generation, allowing for slower cooling fan operation. The objectives of cooler and quieter result in the name Cool'n'Quiet. The technology is similar to Intel's SpeedStep and AMD's own PowerNow!, which were developed with the aim of increasing laptop battery life by reducing power consumption.

The CPU core voltage (VCORE) is the power supply voltage supplied to the processing cores of CPU, GPU, or any other device with a processing core. The amount of power a CPU uses, and thus the amount of heat it dissipates, is the product of this voltage and the current it draws. In modern CPUs, which are CMOS circuits, the current is almost proportional to the clock speed, the CPU drawing almost no current between clock cycles.

Enhanced SpeedStep is a series of dynamic frequency scaling technologies built into some Intel microprocessors that allow the clock speed of the processor to be dynamically changed by software. This allows the processor to meet the instantaneous performance needs of the operation being performed, while minimizing power draw and heat generation. EIST was introduced in several Prescott 6 series in the first quarter of 2005, namely the Pentium 4 660. Intel Speed Shift Technology (SST) was introduced in Intel Skylake Processor.

<span class="mw-page-title-main">AMD APU</span> Series of microprocessors by AMD

AMD Accelerated Processing Unit (APU), formerly known as Fusion, is a series of 64-bit microprocessors from Advanced Micro Devices (AMD), combining a general-purpose AMD64 central processing unit (CPU) and 3D integrated graphics processing unit (IGPU) on a single die.

Dynamic frequency scaling is a power management technique in computer architecture whereby the frequency of a microprocessor can be automatically adjusted "on the fly" depending on the actual needs, to conserve power and reduce the amount of heat generated by the chip. Dynamic frequency scaling helps preserve battery on mobile devices and decrease cooling cost and noise on quiet computing settings, or can be useful as a security measure for overheated systems.

In computer architecture, dynamic voltage scaling is a power management technique in which the voltage used in a component is increased or decreased, depending upon circumstances. Dynamic voltage scaling to increase voltage is known as overvolting; dynamic voltage scaling to decrease voltage is known as undervolting. Undervolting is done in order to conserve power, particularly in laptops and other mobile devices, where energy comes from a battery and thus is limited, or in rare cases, to increase reliability. Overvolting is done in order to support higher frequencies for performance.

AMD PowerPlay is the brand name for a set of technologies for the reduction of the energy consumption implemented in several of AMD's graphics processing units and APUs supported by their proprietary graphics device driver "Catalyst". AMD PowerPlay is also implemented into ATI/AMD chipsets which integrated graphics and into AMD's Imageon handheld chipset, that was sold to Qualcomm in 2008.

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. This rate is typically measured by performance on the LINPACK benchmark when trying to compare between computing systems: an example using this is the Green500 list of supercomputers. Performance per watt has been suggested to be a more sustainable measure of computing than Moore's Law.

Low-power electronics are electronics, such as notebook processors, that have been designed to use less electric power than usual, often at some expense. In the case of notebook processors, this expense is processing power; notebook processors usually consume less power than their desktop counterparts, at the expense of lower processing power.

<span class="mw-page-title-main">GPU switching</span> Mechanism for computers with multiple graphic controllers

GPU switching is a mechanism used on computers with multiple graphic controllers. This mechanism allows the user to either maximize the graphic performance or prolong battery life by switching between the graphic cards. It is mostly used on gaming laptops which usually have an integrated graphic device and a discrete video card.

Electronic systems’ power consumption has been a real challenge for Hardware and Software designers as well as users especially in portable devices like cell phones and laptop computers. Power consumption also has been an issue for many industries that use computer systems heavily such as Internet service providers using servers or companies with many employees using computers and other computational devices. Many different approaches have been discovered by researchers to estimate power consumption efficiently. This survey paper focuses on the different methods where power consumption can be estimated or measured in real-time.

In semiconductor electronics, Dennard scaling, also known as MOSFET scaling, is a scaling law which states roughly that, as transistors get smaller, their power density stays constant, so that the power use stays in proportion with area; both voltage and current scale (downward) with length. The law, originally formulated for MOSFETs, is based on a 1974 paper co-authored by Robert H. Dennard, after whom it is named.

<span class="mw-page-title-main">AMD PowerTune</span> Brand name by AMD

AMD PowerTune is a series of dynamic frequency scaling technologies built into some AMD GPUs and APUs that allow the clock speed of the processor to be dynamically changed by software. This allows the processor to meet the instantaneous performance needs of the operation being performed, while minimizing power draw, heat generation and noise avoidance. AMD PowerTune aims to solve thermal design power and performance constraints.

In computing, energy proportionality is a measure of the relationship between power consumed in a computer system, and the rate at which useful work is done. If the overall power consumption is proportional to the computer's utilization, then the machine is said to be energy proportional. Equivalently stated, for an idealized energy proportional computer, the overall energy per operation is constant for all possible workloads and operating conditions.

<span class="mw-page-title-main">Adaptive voltage scaling</span>

Adaptive voltage scaling (AVS) is a closed-loop dynamic power minimization technique that adjusts the voltage supplied to a computer chip to match the chip's power needs during operation. Many computer chips, especially those in mobile devices or Internet of things devices are constrained by the power available and face varying workloads. In other situations a chip may be constrained by the amount of heat it is allowed to generate. In addition, individual chips can vary in their efficiency due to many factors, including minor differences in manufacturing conditions. AVS allows the voltage supplied to the chip, and therefore its power consumption, to be continuously adjusted to be appropriate to the workload and the parameters of the specific chip. This is accomplished by integrating a device that monitors the performance of the chip into the chip, which then provides information to a power controller.

<span class="mw-page-title-main">Zen (first generation)</span> 2017 AMD 14-nanometre processor microarchitecture

Zen is the codename for the first iteration in a family of computer processor microarchitectures of the same name from AMD. It was first used with their Ryzen series of CPUs in February 2017. The first Zen-based preview system was demonstrated at E3 2016, and first substantially detailed at an event hosted a block away from the Intel Developer Forum 2016. The first Zen-based CPUs, codenamed "Summit Ridge", reached the market in early March 2017, Zen-derived Epyc server processors launched in June 2017 and Zen-based APUs arrived in November 2017.

References

  1. ↑ "AMD PowerNow! Technology with optimized power management". AMD. Retrieved 2009-04-23.
  2. ↑ "IBM EnergyScale for POWER6 Processor-Based Systems". IBM. Retrieved 2009-04-23.
  3. ↑ "AMD Cool'n'Quiet Technology Overview". AMD. Retrieved 2009-04-23.
  4. ↑ "What is GPU computing". Nvidia.
  5. ↑ "Dynamic voltage and frequency scaling framework for low-power embedded GPUs", Daecheol You et al., Electronics Letters (Volume:48, Issue: 21 ), 2012.
  6. ↑ "Effects of Dynamic Voltage and Frequency Scaling on a K20 GPU", Rong Ge et al., 42nd International Conference on Parallel Processing Pages 826-833, 2013.
  7. ↑ "GreenGPU: A Holistic Approach to Energy Efficiency in GPU-CPU Heterogeneous Architectures", Kai Ma et al., 41st International Conference on Parallel Processing Pages 48-57, 2012.
  8. ↑ "Power and performance analysis of GPU-accelerated systems", Yuki Abe et al., USENIX conference on Power-Aware Computing and Systems Pages 10-10, 2012.
  9. ↑ "Design challenges of technology scaling", Borkar, S., IEEE Micro (Volume:19, Issue: 4 ), 1999.
  10. ↑ "Run-time power-gating in caches of GPUs for leakage energy savings", Yue Wang et al., Design, Automation & Test in Europe Conference & Exhibition (DATE), 2012
  11. ↑ "A Predictive Shutdown Technique for GPU Shader Processors", Po-Han Wang et al., Computer Architecture Letters (Volume: 8, Issue: 1 ), 2009
  12. ↑ "Power gating strategies on GPUs", Po-Han Wang et al., ACM Transactions on Architecture and Code Optimization (TACO) Volume 8 Issue 3, 2011
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.