CPU power dissipation

Last updated July 16, 2020

Central processing unit power dissipation or CPU power dissipation is the process in which central processing units (CPUs) consume electrical energy, and dissipate this energy in the form of heat due to the resistance in the electronic circuits.

Power management

Designing CPUs that perform tasks efficiently without overheating is a major consideration of nearly all CPU manufacturers to date. Some CPU implementations use very little power; for example, the CPUs in mobile phones often use just a few watts of electricity,^[1] while some microcontrollers used in embedded systems may consume only a few milliwatts or even as little as a few microwatts. In comparison, CPUs in general-purpose personal computers, such as desktops and laptops, dissipate significantly more power because of their higher complexity and speed. These microelectronic CPUs may consume power in the order of tens of watts, or even hundreds of watts. Historically, early CPUs implemented with vacuum tubes consumed power on the order of many kilowatts.

CPUs for desktop computers typically use a significant portion of the power consumed by the computer. Other major uses include fast video cards, which contain graphics processing units,^[2] and power supplies. In laptops, the LCD's backlight also uses a significant portion of overall power. While energy-saving features have been instituted in personal computers for when they are idle, the overall consumption of today's high-performance CPUs is considerable. This is in strong contrast with the much lower energy consumption of CPUs designed for low-power devices. One such CPU, the Intel XScale, can run at 600 MHz consuming under 1 W of power, whereas Intel x86 PC processors in the same performance bracket consume a few times more energy.

There are some engineering reasons for this pattern.

For a given device, operating at a higher clock rate may require more power. Reducing the clock rate or undervolting usually reduces energy consumption; it is also possible to undervolt the microprocessor while keeping the clock rate the same.^[3]
New features generally require more transistors, each of which uses power. Turning unused areas off saves energy, such as through clock gating.
As a processor model's design matures, smaller transistors, lower-voltage structures, and design experience may reduce energy consumption.

Processor manufacturers usually release two power consumption numbers for a CPU:

typical thermal power, which is measured under normal load. (for instance, AMD's Average CPU power)
maximum thermal power, which is measured under a worst-case load

For example, the Pentium 4 2.8 GHz has 68.4 W typical thermal power and 85 W maximum thermal power. When the CPU is idle, it will draw far less than the typical thermal power. Datasheets normally contain the thermal design power (TDP), which is the maximum amount of heat generated by the CPU, which the cooling system in a computer is required to dissipate. Both Intel and Advanced Micro Devices (AMD) have defined TDP as the maximum heat generation for thermally significant periods, while running worst-case non-synthetic workloads; thus, TDP is not reflecting the actual maximum power of the processor. This ensures the computer will be able to handle essentially all applications without exceeding its thermal envelope, or requiring a cooling system for the maximum theoretical power (which would cost more but in favor of extra headroom for processing power).^[4]^[5]

In many applications, the CPU and other components are idle much of the time, so idle power contributes significantly to overall system power usage. When the CPU uses power management features to reduce energy use, other components, such as the motherboard and chipset, take up a larger proportion of the computer's energy. In applications where the computer is often heavily loaded, such as scientific computing, performance per watt (how much computing the CPU does per unit of energy) becomes more significant.

Sources

There are several factors contributing to the CPU power consumption; they include dynamic power consumption, short-circuit power consumption, and power loss due to transistor leakage currents:

$P_{cpu}=P_{dyn}+P_{sc}+P_{leak}$

The dynamic power consumption originates from the activity of logic gates inside a CPU. When the logic gates toggle, energy is flowing as the capacitors inside them are charged and discharged. The dynamic power consumed by a CPU is approximately proportional to the CPU frequency, and to the square of the CPU voltage:^[6]

P_{dyn}=CV^{2}f

where $C$ is the switched load capacitance, $f$ is frequency, and $V$ is voltage.^[7]

When logic gates toggle, some transistors inside may change states. As this takes a finite amount of time, it may happen that for a very brief amount of time some transistors are conducting simultaneously. A direct path between the source and ground then results in some short-circuit power loss. The magnitude of this power is dependent on the logic gate, and is rather complex to model on a macro level.

Power consumption due to leakage power emanates at a micro-level in transistors. Small amounts of currents are always flowing between the differently doped parts of the transistor. The magnitude of these currents depend on the state of the transistor, its dimensions, physical properties and sometimes temperature. The total amount of leakage currents tends to inflate for increasing temperature and decreasing transistor sizes.

Both dynamic and short-circuit power consumption are dependent on the clock frequency, while the leakage current is dependent on the CPU supply voltage. It has been shown that the energy consumption of a program shows convex energy behavior, meaning that there exists an optimal CPU frequency at which energy consumption is minimal.^[8]

Reduction

Power consumption can be reduced in several ways,^{[ citation needed ]} including the following:

Voltage reduction – dual-voltage CPUs, dynamic voltage scaling, undervolting, etc.
Frequency reduction – underclocking, dynamic frequency scaling, etc.
Capacitance reduction – increasingly integrated circuits that replace PCB traces between two chips with relatively lower-capacitance on-chip metal interconnect between two sections of a single integrated chip; low-k dielectric, etc.
Techniques such as clock gating and globally asynchronous locally synchronous, which can be thought of as reducing the capacitance switched on each clock tick, or can be thought of as locally reducing the clock frequency in some sections of the chip
Various techniques to reduce the switching activity – number of transitions the CPU drives into off-chip data buses, such as non-multiplexed address bus, bus encoding such as Gray code addressing,^[9] or value cache encoding such as power protocol^[10]
Sacrificing transistor density for higher frequencies.
Layering heat-conduction zones within the CPU framework ("Christmassing the Gate").
Recycling at least some of that energy stored in the capacitors (rather than dissipating it as heat in transistors) – adiabatic circuit, energy recovery logic, etc.
Optimizing machine code - by implementing compiler optimizations that schedules clusters of instructions using common components, the CPU power used to run an application can be significantly reduced.^[11]

Clock frequencies and multi-core chip designs

Historically, processor manufacturers consistently delivered increases in clock rates and instruction-level parallelism, so that single-threaded code executed faster on newer processors with no modification.^[12] More recently, in order to manage CPU power dissipation, processor makers favor multi-core chip designs, thus software needs to be written in a multi-threaded or multi-process manner to take full advantage of such hardware. Many multi-threaded development paradigms introduce overhead, and will not see a linear increase in speed when compared to the number of processors. This is particularly true while accessing shared or dependent resources, due to lock contention. This effect becomes more noticeable as the number of processors increases.

Recently, IBM has been exploring ways to distribute computing power more efficiently by mimicking the distributional properties of the human brain.^[13]

CPU overheating

Processor can be damaged from overheating, but vendors protect processors with operational safeguards such as throttling and automatic shutdown. When a core exceeds the set throttle temperature, processors can reduce power to maintain a safe temperature level and if the processor is unable to maintain a safe operating temperature through throttling actions, it will automatically shut down to prevent permanent damage. ^[14]

Related Research Articles

A central processing unit (CPU), also called a central processor or main processor, is the electronic circuitry within a computer that executes instructions that make up a computer program. The CPU performs basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions in the program. The computer industry used the term "central processing unit" as early as 1955. Traditionally, the term "CPU" refers to a processor, more specifically to its processing unit and control unit (CU), distinguishing these core elements of a computer from external components such as main memory and I/O circuitry.

Processor design is the design engineering task of creating a processor, a key component of computer hardware. It is a subfield of computer engineering and electronics engineering (fabrication). The design process involves choosing an instruction set and a certain execution paradigm and results in a microarchitecture, which might be described in e.g. VHDL or Verilog. For microprocessor design, this description is then manufactured employing some of the various semiconductor device fabrication processes, resulting in a die which is bonded onto a chip carrier. This chip carrier is then soldered onto, or inserted into a socket on, a printed circuit board (PCB).

Complementary metal–oxide–semiconductor (CMOS), also known as complementary-symmetry metal–oxide–semiconductor (COS-MOS), is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions. CMOS technology is used for constructing integrated circuit (IC) chips, including microprocessors, microcontrollers, memory chips, and other digital logic circuits, and replaced earlier transistor-transistor logic (TTL) technology.

Overclocking 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 and/or over-specification voids any warranty, however there are an increasing number of manufacturers that will allow overclocking as long as performed (relatively) safely.

In electronics and especially synchronous digital circuits, a clock signal oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits.

The Pentium M is a family of mobile 32-bit single-core x86 microprocessors introduced in March 2003 and forming a part of the Intel Carmel notebook platform under the then new Centrino brand. The Pentium M processors had a maximum thermal design power (TDP) of 5–27 W depending on the model, and were intended for use in laptops. They evolved from the core of the last Pentium III–branded CPU by adding the front-side bus (FSB) interface of Pentium 4, an improved instruction decoding and issuing front end, improved branch prediction, SSE2 support, and a much larger cache. The first Pentium M–branded CPU, code-named Banias, was followed by Dothan. The Pentium M-branded processors were succeeded by the Core-branded dual-core mobile Yonah CPU with a modified microarchitecture.

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 and compatibility. Underclocking may be implemented by the factory, but many computers and components may be underclocked by the end user.

Power management is a feature of some electrical appliances, especially copiers, computers, CPUs, 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. This supersedes APM. All recent (consumer) computers have ACPI support.

The thermal design power (TDP), sometimes called thermal design point, is the maximum amount of heat generated by a computer chip or component that the cooling system in a computer is designed to dissipate under any workload.

In computer engineering, a logic family may refer to one of two related concepts. A logic family of monolithic digital integrated circuit devices is a group of electronic logic gates constructed using one of several different designs, usually with compatible logic levels and power supply characteristics within a family. Many logic families were produced as individual components, each containing one or a few related basic logical functions, which could be used as "building-blocks" to create systems or as so-called "glue" to interconnect more complex integrated circuits. A "logic family" may also refer to a set of techniques used to implement logic within VLSI integrated circuits such as central processors, memories, or other complex functions. Some such logic families use static techniques to minimize design complexity. Other such logic families, such as domino logic, use clocked dynamic techniques to minimize size, power consumption and delay.

A voltage regulator module (VRM), sometimes called processor power module (PPM), is a buck converter that provides a microprocessor the appropriate supply voltage, converting +5 V or +12 V to a much lower voltage required by the CPU, allowing processors with different supply voltage to be mounted on the same motherboard. On personal computer (PC) systems, the VRM is typically made up of power MOSFET devices.

The CPU core voltage (V_CORE) is the power supply voltage supplied to the CPU, GPU, or other device containing 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.

The Intel Core microarchitecture is a multi-core processor microarchitecture unveiled by Intel in Q1 2006. It is based on the Yonah processor design and can be considered an iteration of the P6 microarchitecture introduced in 1995 with Pentium Pro. High power consumption and heat intensity, the resulting inability to effectively increase clock speed, and other shortcomings such as an inefficient pipeline were the primary reasons why Intel abandoned the NetBurst microarchitecture and switched to a completely different architectural design, delivering high efficiency through a small pipeline rather than high clock speeds. The Core microarchitecture initially did not reach the clock speeds of the NetBurst microarchitecture, even after moving to 45 nm lithography. However after many generations of successor microarchitectures which used Core as their basis, Intel managed to eventually surpass the clock speeds of Netburst with the Devil's Canyon microarchitecture reaching a base frequency of 4 GHz and a maximum tested frequency of 4.4 GHz using 22 nm lithography.

In integrated circuit design, dynamic logic is a design methodology in combinatory logic circuits, particularly those implemented in MOS technology. It is distinguished from the so-called static logic by exploiting temporary storage of information in stray and gate capacitances. It was popular in the 1970s and has seen a recent resurgence in the design of high speed digital electronics, particularly computer CPUs. Dynamic logic circuits are usually faster than static counterparts, and require less surface area, but are more difficult to design. Dynamic logic has a higher toggle rate than static logic but the capacitive loads being toggled are smaller so the overall power consumption of dynamic logic may be higher or lower depending on various tradeoffs. When referring to a particular logic family, the dynamic adjective usually suffices to distinguish the design methodology, e.g. dynamic CMOS or dynamic SOI design.

Dynamic frequency scaling is a 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. Dynamic frequency scaling is used in all ranges of computing systems, ranging from mobile systems to data centers to reduce the power at the times of low workload.

Dynamic voltage scaling is a power management technique in computer architecture, where 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 increase computer performance.

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 tend to consume less power than their desktop counterparts, at the expense of lower processing power.

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.

AMD Turbo Core a.k.a. AMD Core Performance Boost (CPB) is a technology implemented by AMD that allows the processor to dynamically adjust and control the processor operating frequency in certain versions of its processors which allows for increased performance when needed while maintaining lower power and thermal parameters during normal operation. AMD Turbo Core technology has been implemented beginning with the Phenom II X6 microprocessors based on the AMD K10 microarchitecture. AMD Turbo Core is available with some AMD A-Series accelerated processing units.

References

↑ Zhang, Yifan; Liu, Yunxin; Zhuang, Li; Liu, Xuanzhe; Zhao, Feng; Li, Qun. Accurate CPU Power Modeling for Multicore Smartphones (Report). Microsoft Research. MSR-TR-2015-9.
↑ Mittal, Sparsh; Vetter, Jeffrey S. (2014). "A Survey of Methods for Analyzing and Improving GPU Energy Efficiency". ACM Computing Surveys. 47 (2): 1–23. arXiv: 1404.4629 . doi:10.1145/2636342.
↑ Cutress, Ian (2012-04-23). "Undervolting and Overclocking on Ivy Bridge". anandtech.com.
↑ Chin, Mike (2004-06-15). "Athlon 64 for Quiet Power". silentpcreview.com. p. 3. Retrieved 2013-12-21. Thermal Design Power (TDP) should be used for processor thermal solution design targets. The TDP is not the maximum power that the processor can dissipate.
↑ Cunningham, Andrew (2013-01-14). "The technical details behind Intel's 7 Watt Ivy Bridge CPUs". Ars Technica. Retrieved 2013-01-14. In Intel's case, a specified chip's TDP has less to do with the amount of power a chip needs to use (or can use) and more to do with the amount of power the computer's fan and heatsink need to be able to dissipate while the chip is under sustained load. Actual power usage can be higher or (much) lower than TDP, but the figure is intended to give guidance to engineers designing cooling solutions for their products.
↑ "Enhanced Intel SpeedStep Technology for the Intel Pentium M Processor (White Paper)" (PDF). Intel Corporation. March 2004. Archived from the original (PDF) on 2015-08-12. Retrieved 2013-12-21.
↑ Jan M. Rabaey; Massoud Pedram; editors. "Low Power Design Methodologies". 2012. p. 133.
↑ De Vogeleer, Karel; Memmi, Gerard; Jouvelot, Pierre; Coelho, Fabien (2013-09-09). "The Energy/Frequency Convexity Rule: Modeling and Experimental Validation on Mobile Devices". arXiv: 1401.4655 [cs.OH].
↑ Su, Ching-Long; Tsui, Chi-Ying; Despain, Alvin M. (1994). Low Power Architecture Design and Compilation Techniques for High-Performance Processors (PDF) (Report). Advanced Computer Architecture Laboratory. ACAL-TR-94-01.
↑ Basu, K.; Choudhary, A.; Pisharath, J.; Kandemir, M. (2002). Power Protocol: Reducing Power Dissipation on Off-Chip Data Buses (PDF). Proceedings of the 35th Annual International Symposium on Microarchitecture (MICRO). pp. 345–355. CiteSeerX 10.1.1.115.9946 . doi:10.1109/MICRO.2002.1176262. ISBN 978-0-7695-1859-6.
↑ Al-Khatib, Zaid; Abdi, Samar (2015-04-13). Operand-Value-Based Modeling of Dynamic Energy Consumption of Soft Processors in FPGA. Applied Reconfigurable Computing. Lecture Notes in Computer Science. 9040. Springer, Cham. pp. 65–76. doi:10.1007/978-3-319-16214-0_6. ISBN 978-3-319-16213-3.
↑ Sutter, Herb (2005). "The Free Lunch Is Over: A Fundamental Turn Toward Concurrency in Software". Dr. Dobb's Journal . 30 (3).
↑ Johnson, R. Colin (2011-08-18). "IBM demos cognitive computer chips". EE Times . Retrieved 2011-10-01.
↑ "Frequently Asked Questions About Temperature for Intel® Processors".

External links

CPU Reference for all vendors. Process node, die size, speed, power, instruction set, etc.
Processor Electrical Specifications
SizingLounge – online calculation tool for server energy costs
For specification on Intel processors
Making x86 Run Cool, 2001-04-15, by Paul DeMone

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[1] Zhang, Yifan; Liu, Yunxin; Zhuang, Li; Liu, Xuanzhe; Zhao, Feng; Li, Qun. Accurate CPU Power Modeling for Multicore Smartphones (Report). Microsoft Research. MSR-TR-2015-9.

[2] Mittal, Sparsh; Vetter, Jeffrey S. (2014). "A Survey of Methods for Analyzing and Improving GPU Energy Efficiency". ACM Computing Surveys. 47 (2): 1–23. arXiv: 1404.4629 . doi:10.1145/2636342.

[3] Cutress, Ian (2012-04-23). "Undervolting and Overclocking on Ivy Bridge". anandtech.com.

[4] Chin, Mike (2004-06-15). "Athlon 64 for Quiet Power". silentpcreview.com. p. 3. Retrieved 2013-12-21. Thermal Design Power (TDP) should be used for processor thermal solution design targets. The TDP is not the maximum power that the processor can dissipate.

[5] Cunningham, Andrew (2013-01-14). "The technical details behind Intel's 7 Watt Ivy Bridge CPUs". Ars Technica. Retrieved 2013-01-14. In Intel's case, a specified chip's TDP has less to do with the amount of power a chip needs to use (or can use) and more to do with the amount of power the computer's fan and heatsink need to be able to dissipate while the chip is under sustained load. Actual power usage can be higher or (much) lower than TDP, but the figure is intended to give guidance to engineers designing cooling solutions for their products.

[6] "Enhanced Intel SpeedStep Technology for the Intel Pentium M Processor (White Paper)" (PDF). Intel Corporation. March 2004. Archived from the original (PDF) on 2015-08-12. Retrieved 2013-12-21.

[7] Jan M. Rabaey; Massoud Pedram; editors. "Low Power Design Methodologies". 2012. p. 133.

[8] De Vogeleer, Karel; Memmi, Gerard; Jouvelot, Pierre; Coelho, Fabien (2013-09-09). "The Energy/Frequency Convexity Rule: Modeling and Experimental Validation on Mobile Devices". arXiv: 1401.4655 [cs.OH].

[9] Su, Ching-Long; Tsui, Chi-Ying; Despain, Alvin M. (1994). Low Power Architecture Design and Compilation Techniques for High-Performance Processors (PDF) (Report). Advanced Computer Architecture Laboratory. ACAL-TR-94-01.

[10] Basu, K.; Choudhary, A.; Pisharath, J.; Kandemir, M. (2002). Power Protocol: Reducing Power Dissipation on Off-Chip Data Buses (PDF). Proceedings of the 35th Annual International Symposium on Microarchitecture (MICRO). pp. 345–355. CiteSeerX 10.1.1.115.9946 . doi:10.1109/MICRO.2002.1176262. ISBN 978-0-7695-1859-6.

[11] Al-Khatib, Zaid; Abdi, Samar (2015-04-13). Operand-Value-Based Modeling of Dynamic Energy Consumption of Soft Processors in FPGA. Applied Reconfigurable Computing. Lecture Notes in Computer Science. 9040. Springer, Cham. pp. 65–76. doi:10.1007/978-3-319-16214-0_6. ISBN 978-3-319-16213-3.

[12] Sutter, Herb (2005). "The Free Lunch Is Over: A Fundamental Turn Toward Concurrency in Software". Dr. Dobb's Journal . 30 (3).

[13] Johnson, R. Colin (2011-08-18). "IBM demos cognitive computer chips". EE Times . Retrieved 2011-10-01.

[14] "Frequently Asked Questions About Temperature for Intel® Processors".