White Paper - Power Management in Intel Architecture Servers

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Glossary
Advanced Configuration and Power Interface (ACPI): ACPI is an open-standard specification for unified OS-centric device configuration and power
management. It brings power management into OS control, as opposed to BIOS central systems. ASL is the ACPI Source Language used for specifying the
desired device behavior.
C-state: The processor C-state is the processor’s capability to go into various low power idle states (with varying wake-up latencies). Intel architecture-based
processors have several C-states representing parts that can be switched off to save power. C0 is the operational state, meaning that the CPU is doing useful
work. C1 is the first idle state: The clock running the processor is gated; that is, the clock is prevented from reaching the core, effectively shutting it down in an
operational sense. C2 is the second idle state: The external I/O Controller Hub blocks interrupts to the processor. And so on with C3, C4, and others.
P-states: The processor P-state is the capability of running the processor at different voltage and/or frequency levels. Generally, P0 is the highest state resulting
in maximum performance, while P1, P2, and so on, will save power but at some penalty to CPU performance.
Server Management Interrupt (SMI): SMI is a special-purpose interrupt that can perform various system management functions including a system’s Power controls.
Demand Based Switching (DBS): DBS is a power-management technology in which the applied voltage and clock speed for a processor are kept to the minimum
necessary to allow optimum performance of the required operations. A microprocessor equipped with DBS operates at a reduced p-state (voltage and clock speed)
until more processing power is actually required. DBS helps to reduce average system power consumption and potentially improves system acoustics.
Intel® Intelligent Power Node Manager (NM): NM is a power-management policy engine that is embedded in Intel® server chipsets. It works with BIOS and OS
power management (OSPM) to dynamically adjust platform power to achieve maximum performance and power at a server level, by setting time-based power limit
policies, and adjusting P-states. If this power limit can’t be reached, an alert or shut-down action can be initiated.
Intel® Turbo Boost Technology: Intel Turbo Boost Technology allows a processor’s cores to run faster than the base operating frequency if the package is
operating below its power, current, and temperature specification limits. Intel Turbo Boost Technology is activated when the OS requests the highest processor
performance state (P0). Maximum frequency depends on the number of active cores. The amount of time the processor spends in the Intel Turbo Boost Technology
state depends on the workload and operating environment, providing the extra performance. Intel Turbo Boost Technology increases the performance of both
multi-threaded and single-threaded workloads.
References
www�intel�com/support/processors/sb/CS-028855�htm
http://communities�intel�com/servlet/JiveServlet/previewBody/1492-102-1-1723/Node%20Manager%20Baidu%20POC%20
WhitePaper%20-%20External�pdf
www�intel�com/pressroom/archive/releases/20080819comp�htm
http://communities�intel�com/openport/blogs/server/2008/04/11/dynamic-power-management-has-significant-values-a-baidu-case-study