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    SubjectRe: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)
    On Wed, 2 Jun 2010 11:05:18 -0700
    Brian Swetland <> wrote:

    > On Wed, Jun 2, 2010 at 1:06 AM, Neil Brown <> wrote:
    > > On Wed, 2 Jun 2010 00:05:14 -0700
    > > Arve Hjønnevåg <> wrote:
    > >> > The user-space suspend daemon avoids losing wake-events by using
    > >> > fcntl(F_OWNER) to ensure it gets a signal whenever any important wake-event
    > >> > is ready to be read by user-space.  This may involve:
    > >> >  - the one daemon processing all wake events
    > >>
    > >> Wake up events are not all processed by one daemon.
    > >
    > > Not with your current user-space code, no.  Are you saying that you are not
    > > open to any significant change in the Android user-space code?  That would
    > > make the situation a lot harder to resolve.
    > There are many wakeup events possible in a typical system --
    > keypresses or other input events, network traffic, telephony events,
    > media events (fill audio buffer, fill video decoder buffer, etc), and
    > I think requiring that all wakeup event processing bottleneck through
    > a single userspace process is non-optimal here.

    Just to be clear: I'm not suggesting all wake-events need to go through one
    process. That was just one example of how the interface I proposed could be
    used. There were two other examples.
    However one process would need to know about any wakeup event that happens.
    I don't think that needs to be a significant bottleneck, but I don't really
    know enough about all the requirement to try devising a demonstration.

    > The current suspend-blocker proposal already involves userspace
    > changes (it's different than our existing wakelock interface), and
    > we're certainly not opposed to any/all userspace changes on principle,
    > but on the other hand we're not interested in significant reworks of
    > userspace unless they actually improve the situation somehow. I think
    > bottlenecking events through a central daemon would represent a step
    > backwards.

    I guess it becomes an question of economics for you then. Does the cost of
    whatever user-space changes are required exceed the value of using an upstream
    kernel? Both the cost and the value would be very hard to estimate in
    advance. I don't envy you the decision...

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