Re: Attempted summary of suspend-blockers LKML thread, take two

From: Paul E. McKenney
Date: Thu Aug 05 2010 - 19:35:51 EST

On Thu, Aug 05, 2010 at 06:37:15AM -0700, Brian Swetland wrote:
> On Thu, Aug 5, 2010 at 6:18 AM, <david@xxxxxxx> wrote:
> > On Wed, 4 Aug 2010, Paul E. McKenney wrote:
> >
> >> Continuing to rush in where angels fear to tread...
> >
> > here here :-)
> >
> >> o       "PM-driving application" are applications that are permitted
> >>        to acquire suspend blockers on Android.  Verion 8 of the
> >>        suspend-blocker patch seems to use group permissions to determine
> >>        which applications are classified as power aware.  More generally,
> >>        PM-driving applications seem to be those that have permission
> >>        to exert some control over the system's sleep state.
> >>
> >>        Note that an application might be power-oblivious on one Android
> >>        device and PM-driving on another, depending on whether the user
> >>        allows that application to acquire suspend blockers.  The
> >>        classification might even change over time.  For example, a
> >>        user might give an application PM-driving status initially,
> >>        but change his or her mind after some experience with that
> >>        application.
> >
> > One thing that I think it's important to document here is theinformation
> > that Brian provided in response to your question about how many (or actually
> > how few) applications fall into this catefory
> I think I need to clarify here. When I say "app" in the context of
> Android, I mean "an application running under the Android app model --
> sandboxed under a per-app or app-group uid", not "a process". The
> vast majority of processes on an Android device are "apps" in this
> sense, but some (usually low level services or daemons) are not. Also
> I use "wakelock" as a place holder for "suspend blocker" or whatever
> exact API we're trying to hash out here, because it's shorter and I'm
> lazy.
> Any app may obtain a wakelock through the standard Android APIs,
> provided it has permission to do so. In the current implementation,
> apps obtain wakelocks via making a binder RPC call to the power
> manager service which tracks high level wakelocks (for apps!) and
> backs them by a single kernel wakelock. Access control is at the RPC
> level. This implementation could be changed to have the app API
> simply open /dev/suspendblock or whatnot, with access control enforced
> by unix permissions (the framework would arrange for apps with the
> android "can block sleep" permission to be in a unix group that has
> access to the device).
> For native services (native daemons that run "underneath" the android
> app framework -- for example the media service, the radio interface,
> etc), the kernel interface is used directly (ok, usually via a very
> thin C convenience wrapper).

Thank you for the added detail on Android user-space operation!!!

Thanx, Paul

> Brian
> > Quote:
> >
> >> I should have asked this earlier...  What exactly are the apps'
> >> compatibility constraints?  Source-level APIs?  Byte-code class-library
> >> invocations?  C/C++ dynamic linking?  C/C++ static linking (in other
> >> words, syscall)?
> >
> > For Java/Dalvik apps, the wakelock API is pertty high level -- it
> > talks to a service via RPC (Binder) that actually interacts with the
> > kernel.  Changing the basic kernel<->userspace interface (within
> > reason) is not unthinkable.  For example, Arve's suspend_blocker patch
> > provides a device interface rather than the proc interface the older
> > wakelock patches use.  We'd have to make some userspace changes to
> > support that but they're pretty low level and minor.
> >
> > In the current model, only a few processes need to specifically
> > interact with the kernel (the power management service in the
> > system_server, possibly the media_server and the radio interface
> > glue).  A model where every process needs to have a bunch of
> > instrumentation is not very desirable from our point of view.  We
> > definitely do need reasonable statistics in order to enable debugging
> > and to enable reporting to endusers (through the Battery Usage UI)
> > what's keeping the device awake.
> >
> > Brian
> >
> >
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