Intel® 64 and IA-32 Architectures Optimization Reference Manual

POWER OPTIMIZATION FOR MOBILE USAGES• In an Intel Core Solo, Intel Core Duo processor or a processor based on Intel Coremicroarchitecture, after staying in C4 for an extended time, the processor mayenter into a Deep C4 state to save additional static power.The processor reduces voltage to the minimum level required to safely maintainprocessor context. Although exiting from a deep C4 state may require warming thecache, the performance penalty may be low enough such that the benefit of longerbattery life outweighs the latency of the deep C4 state.10.4 GUIDELINES FOR EXTENDING BATTERY LIFEFollow the guidelines below to optimize to conserve battery life and adapt for mobilecomputing usage:• Adopt a power management scheme to provide just-enough (not the highest)performance to achieve desired features or experiences.• Avoid using spin loops.• Reduce the amount of work the application performs while operating on abattery.• Take advantage of hardware power conservation features using ACPI C3 statetype and coordinate processor cores in the same physical processor.• Implement transitions to and from system sleep states (S1-S4) correctly.• Allow the processor to operate at a higher-numbered P-state (lower frequencybut higher efficiency in performance-per-watt) when demand for processorperformance is low.• Allow the processor to enter higher-numbered ACPI C-state type (deeper, lowpowerstates) when user demand for processor activity is infrequent.10.4.1 Adjust Performance to Meet Quality of FeaturesWhen a system is battery powered, applications can extend battery life by reducingthe performance or quality of features, turning off background activities, or both.Implementing such options in an application increases the processor idle time.Processor power consumption when idle is significantly lower than when active,resulting in longer battery life.Example of techniques to use are:• Reducing the quality/color depth/resolution of video and audio playback.• Turning off automatic spell check and grammar correction.• Turning off or reducing the frequency of logging activities.• Consolidating disk operations over time to prevent unnecessary spin-up of thehard drive.• Reducing the amount or quality of visual animations.10-5