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    Subject[RFC][PATCH 0/8] PM: Implement autosleep and "wake locks", take 3
    Hi all,

    Following is the third update of the autosleep patchset.

    Patches [1-4/8] are regarded as v3.5 material, the rest - depending on
    the feedback I get (lack of feedback will be understood as no objections,

    On Wednesday, February 22, 2012, Rafael J. Wysocki wrote:
    > Hi all,
    > After the feedback so far I've decided to follow up with a refreshed patchset.
    > The first two patches from the previous one went to linux-pm/linux-next
    > and I included the recent evdev patch from Arve (with some modifications)
    > to this patchset for completness.
    > On Tuesday, February 07, 2012, Rafael J. Wysocki wrote:
    > > Hi all,
    > >
    > > This series tests the theory that the easiest way to sell a once rejected
    > > feature is to advertise it under a different name.
    > >
    > > Well, there actually are two different features, although they are closely
    > > related to each other. First, patch [6/8] introduces a feature that allows
    > > the kernel to trigger system suspend (or more generally a transition into
    > > a sleep state) whenever there are no active wakeup sources (no, they aren't
    > > called wakelocks). It is called "autosleep" here, but it was called a few
    > > different names in the past ("opportunistic suspend" was probably the most
    > > popular one). Second, patch [8/8] introduces "wake locks" that are,
    > > essentially, wakeup sources which may be created and manipulated by user
    > > space. Using them user space may control the autosleep feature introduced
    > > earlier.
    > >
    > > This also is a kind of a proof of concept for the people who wanted me to
    > > show a kernel-based implementation of automatic suspend, so there you go.
    > > Please note, however, that it is done so that the user space "wake locks"
    > > interface is compatible with Android in support of its user space. I don't
    > > really like this interface, but since the Android's user space seems to rely
    > > on it, I'm fine with using it as is. YMMV.
    > >
    > > Let me say a few words about every patch in the series individually.
    > >
    > > [1/8] - This really is a bug fix, so it's v3.4 material. Nobody has stepped
    > > on this bug so far, but it should be fixed anyway.
    > >
    > > [2/8] - This is a freezer cleanup, worth doing anyway IMO, so v3.4 material too.

    The two patches above have been merged.

    > The above two are in linux-pm/linux-next now. There are a few more fixes
    > related to wakeup sources in there and the patches below are based on that
    > branch.
    > > [3/8] - This is something we can do no problem, although completely optional
    > > without the autosleep feature. Rather necessary with it, though.
    > Now [1/7] - Look for wakeup events in later stages of device suspend.

    [1/8] now - Look for wakeup events later down the suspend code path.

    > > [4/8] - This kind of reintroduces my original idea of using a wait queue for
    > > waiting until there are no wakeup events in progress. Alan convinced me that
    > > it would be better to poll the counter to prevent wakeup_source_deactivate()
    > > from having to call wake_up_all() occasionally (that may be costly in fast
    > > paths), but then quite some people told me that the wait queue migh be
    > > better. I think that the polling will make much less sense with autosleep
    > > and user space "wake locks". Anyway, [4/8] is something we can do without
    > > those things too.
    > Now [2/7] - Use wait queue to signal "no wakeup events in progress"
    > With a couple of improvements suggested by Neil.

    [2/8] now - Use wait queue to signal "no wakeup events in progress" condition.

    > > The patches above were given Sign-off-by tags, because I think they make some
    > > sense regardless of the features introcuded by the remaining patches that in
    > > turn are total RFC.
    > This time all of the patches are signed-off and include the requisite
    > documentation changes (hopefully, I haven't forgotten about anything).
    > > [5/8] - This changes wakeup source statistics so that they are more similar to
    > > the statistics collected for wakelocks on Android. The file those statistics
    > > may be read from is still located in debugfs, though (I don't think it
    > > belongs to proc and its name is different from the analogous Android's file
    > > name anyway). It could be done without autosleep, but then it would be a bit
    > > pointless. BTW, this changes interfaces that _in_ _theory_ may be used by
    > > someone, but I'm not aware of anyone using them. If you are one, I'll be
    > > pleased to learn about that, so please tell me who you are. :-)
    > Now [3/7] - Change wakeup source statistics to follow Android.
    > Rebased and reworked in accordance with the Arve's feedback.

    [3/8] now - Change wakeup source statistics to follow Android.

    [4/8] - Add tracepoints to wakeup_source_{de}activate()

    [5/8] - Teach epoll to use wakeup sources if requested

    This should be sufficient to ensure that a wakeup source will be kept active
    after a wakeup event all the way up to user space without a need to make a
    number of random drivers use wakeup sources.

    > > [6/8] - Autosleep implementation. I think the changelog explains the idea
    > > quite well and the code is really nothing special. It doesn't really add
    > > anything new to the kernel in terms of infrastructure etc., it just uses
    > > the existing stuff to implement an alternative method of triggering system
    > > sleep transitions. Note, though, that the interface here is different
    > > from the Android's one, because Android actually modifies /sys/power/state
    > > to trigger something called "early suspend" (that is never going to be
    > > implemented in the "stock" kernel as long as I have any influence on it) and
    > > we simply can't do that in the mainline.
    > Now [5/7] - Implement opportunistic sleep
    > Rebased and simplified (most notably, I've dropped the "main" wakeup source,
    > since it wasn't really necessary).

    [6/8] now - Implement apportunistic sleep.

    > > [7/8] - This adds a wakeup source statistics that only makes sense with
    > > autosleep and (I believe) is analogous to the Android's prevent_suspend_time
    > > statistics. Nothing really special, but I didn't want
    > > wakeup_source_activate/deactivate() to take a common lock to avoid
    > > congestion.
    > Now [6/7] - Add "prevent autosleep time" statistics to wakeup sources.
    > Rebased.

    [7/8] now - Add "prevent autosleep time" statistics to wakeup sources.

    > > [8/8] - This adds a user space interface to create, activate and deactivate
    > > wakeup sources. Since the files it consists of are called wake_lock and
    > > wake_unlock, to follow Android, the objects the wakeup sources are wrapped
    > > into are called "wakelocks" (for added confusion). Since the interface
    > > doesn't provide any means to destroy those "wakelocks", I added a garbage
    > > collection mechanism to get rid of the unused ones, if any. I also tought
    > > it might be a good idea to put a limit on the number of those things that
    > > user space can operate simultaneously, so I did that too.
    > Now [7/7] - Add user space interface for manipulating wakeup sources.

    [8/8] now - Add user space interface for manipulating wakeup sources.

    > > All of the above has been tested very briefly on my test-bed Mackerel board
    > > and it quite obviously requires more thorough testing, but first I need to know
    > > if it makes sense to spend any more time on it.
    > The above is still accurate, but I also verified that the patches don't break
    > my PC test boxes (at least as long as the new features aren't used ;-)).

    Nothing has changed in that respect, as far as I can say.

    The patches in the following series are available from the autosleep branch in
    the linux-pm tree.


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