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    SubjectRe: [linux-pm] [PATCH 0/8] Suspend block api (version 8)
    On Tue, 2010-06-01 at 14:51 +0100, Matthew Garrett wrote:
    > On Mon, May 31, 2010 at 04:21:09PM -0500, James Bottomley wrote:
    > > You're the one mentioning x86, not me. I already explained that some
    > > MSM hardware (the G1 for example) has lower power consumption in S3
    > > (which I'm using as an ACPI shorthand for suspend to ram) than any
    > > suspend from idle C state. The fact that current x86 hardware has the
    > > same problem may be true, but it's not entirely relevant.
    > As long as you can set a wakeup timer, an S state is just a C state with
    > side effects. The significant one is that entering an S state stops the
    > process scheduler and any in-kernel timers. I don't think Google care at
    > all about whether suspend is entered through an explicit transition or
    > something hooked into cpuidle - the relevant issue is that they want to
    > be able to express a set of constraints that lets them control whether
    > or not the scheduler keeps on scheduling, and which doesn't let them
    > lose wakeup events in the process.

    Exactly, so my understanding of where we currently are is:

    1. pm_qos will be updated to be able to express the android suspend
    blockers as interactivity constraints (exact name TBD, but
    probably /dev/cpu_interactivity)
    2. pm_qos will be updated to be callable from atomic context
    3. pm_qos will be updated to export statistics initially closely
    matching what suspend blockers provides (simple update of the rw

    After this is done, the current android suspend block patch becomes a
    re-expression in kernel space in terms of pm_qos, with the current
    userspace wakelocks being adapted by the android framework into pm_qos
    requirements expressed to /dev/cpu_interactivity (or whatever name is
    chosen). Then opportunistic suspend is either a small add-on kernel
    patch they have in their tree to suspend when the interactivity
    constraint goes to NONE, or it could be done entirely by a userspace
    process. Long term this could migrate to the freezer and suspend from
    idle approach as the various problem timers get fixed.

    I think the big unresolved issue is the stats extension. For android,
    we need just a name written along with the value, so we have something
    to hang the stats off ... current pm_qos userspace users just write a
    value, so the name would be optional. From the kernel, we probably just
    need an additional API that takes a stats name or NULL if none
    (pm_qos_add_request_named()?). Then reading the stats could be done by
    implementing a fops read routine on the misc device.

    Did I miss anything?


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