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    SubjectRe: [linux-pm] [PATCH 0/8] Suspend block api (version 8)
    From
    2010/6/1 Thomas Gleixner <tglx@linutronix.de>:
    >
    > On Mon, 31 May 2010, Arve Hjønnevåg wrote:
    >
    >> On Mon, May 31, 2010 at 2:46 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
    >> > On Mon, 31 May 2010, James Bottomley wrote:
    >> >>
    >> >> For MSM hardware, it looks possible to unify the S and C states by doing
    >> >> suspend to ram from idle but I'm not sure how much work that is.
    >> >
    >> > On ARM, it's not rocket science and we have in tree support for this
    >> > already (OMAP). I have done the same thing on a Samsung part as a
    >> > prove of concept two years ago and it's really easy as the hardware is
    >> > sane. Hint: It's designed for mobile devices :)
    >> >
    >>
    >> We already enter the same power state from idle and suspend on msm. In
    >> the absence of misbehaving apps, the difference in power consumption
    >> is entirely caused by periodic timers in the user-space framework
    >> _and_ kernel. It only takes a few timers triggering per second (I
    >> think 3 if they do no work) to double the average power consumption on
    >> the G1 if the radio is off. We originally added wakelocks because the
    >> hardware we had at the time had much lower power consumption in
    >> suspend then idle, but we still use suspend because it saves power.
    >
    > So how do you differentiate between timers which _should_ fire and
    > those you do not care about ?
    >

    Only alarms are allowed to fire while suspended.

    > We have mechanisms in place to defer timers so the wakeups are
    > minimized. If that's not enough we need to revisit.
    >

    Deferring the the timers forever without stopping the clock can cause
    problems. Our user space code has a lot of timeouts that will trigger
    an error if an app does not respond in time. Freezing everything and
    stopping the clock while suspended is a lot simpler than trying to
    stop individual timers and processes from running.


    --
    Arve Hjønnevåg
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