Power optimization for PC Architecture is vastly different from that for embedded systems such as ARM based PDAs or Cell phones. This is because each embedded chipset has its own unique set of power management features that require a custom flavor of linux built from the ground up. PC based chipsets already have a well established code base in linux, with existing hardware interfaces such as ACPI and HAL; and as they have evolved from desktops into smaller, more portable systems, a wealth of software packages have been created to optimize power.
Each of these packages can be thought of as a power micro-policy controller for a specific subsystem on a linux based platform. For instance cpufreq manages power for the CPU supsystem, or the iwconfig interface manages device specific power for the Network (WLAN) subsystem. Currently all these micro-policy managers function independantly of one another and with little or no information from the user domain. Thus there are two things lacking in linux with regard to power. The first is a centralized policy manager which can gather input from ACPI, the user, and running applications to generate a complete picture of how the device is being used. This information can be used to create macro-policies which can selectively tune or override the systems micro-policy managers to achieve far greater power optimization. The second piece missing is a scheme to create micro-policy managers for all power-hungry subsystems that dont currently support any form of control.
Macro-policy focus is on the usage model
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Where is the user and device (e.g. stationary vs moving, near to vs from from a power source, inside or outside
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When is the device being used (e.g. night vs day)
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How is the device being used (e.g. is the user listening to it, looking at it, controlling it)
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What is the device being used for (e.g. using network, playing audio, displaying video, high vs low performance)
Micro-policy focus is on the subsystem and driver level
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Groupings by power optimization capability
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CPU (single or multi-core)
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Network (LAN, WLAN, WWAN)
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Storage (Harddisk, Flashdisk, DVDROM)
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Human Interface Devices (Mouse, Keyboard, Touchscreen)
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Video (LCD, Graphics card
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Audio (Speakers, Headphones, AC97, HD Audio)
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Wireless Connections (Bluetooth, GPS)
Architecture
The power policy manager for linux is meant to be a universal, cross-platform framework for reducing power consumption in linux based devices; with particular focus on handhelds. It is implemented in three parts: a configuration data layer, a micro policy engine control layer, and a daemon that ties the two together.
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Configuration Layer: Provides “configuration element” messages from a GUI, applications, and system agents which describe the optimization potential in the system. e.g. user focus, device position, handling, and movement, and application needs. The Configuration Element Interface (CEI), will be based on Dbus and can be used by applications or a GUI to provide usage model information to our power manager daemon. Usage model info is intended to help us understand where, when, how, and for what purpose the device is being used. These attributes can help us intelligently regulate power and performance to match the users neds and expectations.
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MPE Layer: Provides “tunable element” control access to all the subsysems on the platform. e.g. LCD brightness, Audio codec, etc. The MPE Interface (MPI), will be used to control any subsystem micro-policy managers which are already available to us. Subsystems are determined as a collection of devices which serve some common purpose that can be optimized for power cleanly. Micro-policy engines will exist for each subsystem we intend to control.
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PPM Daemon: Defines what groupings of configuration elements are configuratble from the GUI, and the mappings between configuration and tunable elements.
Constraints
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No dependence on knowledge of specific applications or drivers
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Should exist entirely in user space so there's no kernel dependency
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Use C as the default programming language
