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    SubjectPower Management framework proposal
    I'm deliberatly breaking the threading on this so that people who have 
    tuned out the hibernation thread can take a look at this.

    below is the proposal that I made at the bottom of one of the posts on the
    hibernation thread.

    the idea is that instead of approaching power management from the point of
    view of the current desktop standard (ACPI), instead this approaches it
    from the point of view of 'what does a tool need to know to do the job' no
    matter what mechanism is actually used to implement the different modes.

    one thing that I didn't put in the original post is that the framework
    that I mention below should work with other types of devices besides ACPI

    CPU clock settings could fit the same API for example (with modeID=0 being
    to hot-unplug the cpu and modeID=1 to initialize the cpu)

    here's the original post:

    in fact, a better abstraction would be something like

    which would return a series of modes (sorted only by modeID)
    modeID, %power_used_in_this_mode, %capability_in_this_mode
    (I would make mode 0 always be complete power off, and mode 1 always be
    full capacity)

    which would return a matrix giving how long it takes to transition from any
    mode to any other mode. this should be a relative number, not an absolute
    number since it will be different at different clock speeds.

    which would take you from whatever mode you are in now to the requested mode.

    most devices would report the simple list of modes


    with a mode_speed matrix of
    0 1
    0|0 1
    1|1 0

    it may be that there is more info needed for the powr management engine to
    decide what modes it wants to put things into, if so identify what type of info
    you need and add another column to the modes list.
    for example:
    you may want to add a flag for 'does this mode allow downstream devices to
    you may want to make a mode for 'this mode doesn't allow any new requests,
    but continues to process pending requests' and have a flag that indicates this

    currently it looks like there's no way to find out what modes are available,
    and you have to know what mode something is in currently before you can request
    it change to a different mode. both of these prevent effective power management
    without encoding intimate knowledge of the capability of the particular
    hardware in your management tool.

    some of this may be discoverable via the ACPI interface (it's not talked about
    much in the devices.txt file), but the mode setting is still wrong.

    note that in the example above it's accpetable for a driver to cache what mode
    it thinks the device is in, but it needs to properly set the new mode even if
    it's cached data is incorrect.

    this approach would allow the transition of ALL drivers to the new mode of
    operation in one fell swoop, and then adding additional power management
    features is just adding to the existing list rather then implementing new

    David Lang
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      Last update: 2007-07-22 08:53    [W:0.020 / U:18.608 seconds]
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