On Wed, Aug 04, 2010 at 04:23:43PM -0700, david@xxxxxxx wrote: > On Wed, 4 Aug 2010, Arve Hj?nnev?g wrote: > > >2010/8/4 <david@xxxxxxx>: > >>On Wed, 4 Aug 2010, Arve Hj?nnev?g wrote: > >> > >>>On Wed, Aug 4, 2010 at 3:31 PM, <david@xxxxxxx> wrote: > >>>> > >>>>On Wed, 4 Aug 2010, Matthew Garrett wrote: > >>>> > >>>>>On Wed, Aug 04, 2010 at 10:51:07PM +0200, Rafael J. Wysocki wrote: > >>>>>> > >>>>>>On Wednesday, August 04, 2010, Matthew Garrett wrote: > >>>>>>> > >>>>>>>No! And that's precisely the issue. Android's existing behaviour could > >>>>>>>be entirely implemented in the form of binary that manually triggers > >>>>>>>suspend when (a) the screen is off and (b) no userspace applications > >>>>>>>have indicated that the system shouldn't sleep, except for the wakeup > >>>>>>>event race. Imagine the following: > >>>>>>> > >>>>>>>1) The policy timeout is about to expire. No applications are holding > >>>>>>>wakelocks. The system will suspend providing nothing takes a wakelock. > >>>>>>>2) A network packet arrives indicating an incoming SIP call > >>>>>>>3) The VOIP application takes a wakelock and prevents the phone from > >>>>>>>suspending while the call is in progress > >>>>>>> > >>>>>>>What stops the system going to sleep between (2) and (3)? cgroups > >>>>>>>don't, > >>>>>>>because the voip app is an otherwise untrusted application that you've > >>>>>>>just told the scheduler to ignore. > >>>>>> > >>>>>>I _think_ you can use the just-merged /sys/power/wakeup_count mechanism > >>>>>>to > >>>>>>avoid the race (if pm_wakeup_event() is called at 2)). > >>>>> > >>>>>Yes, I think that solves the problem. The only question then is whether > >>>>>it's preferable to use cgroups or suspend fully, which is pretty much up > >>>>>to the implementation. In other words, is there a reason we're still > >>>>>having this conversation? :) It'd be good to have some feedback from > >>>>>Google as to whether this satisfies their functional requirements. > >>>> > >>>>the proposal that I nade was not to use cgroups to freeze some processes > >>>>and > >>>>not others, but to use cgroups to decide to ignore some processes when > >>>>deciding if the system is idle, stop everything or nothing. cgroups are > >>>>just > >>>>a way of easily grouping processes (and their children) into different > >>>>groups. > >>>> > >>> > >>>That does not avoid the dependency problem. A process may be waiting > >>>on a resource that a process you ignore owns. I you ignore the process > >>>that owns the resource and enter idle when it is ready to run (or > >>>waiting on a timer), you are still effectively blocking the other > >>>process. > >> > >>and if you don't have a wakelock the same thing will happen. If you expect > > > >Not the same thing. If you don't hold a wakelock the entire system > >will suspend and when it wakes up it continues where it left off. > >Timeout still have time left before they expire. > > in what I'm proposing, if the 'privilaged/trusted" processes are > idle long enough the entire system will suspend, and when it wakes > up everything will continue to process normally > > >>the process to take a while you can set a timeout to wake up every 30 > >>seconds or so and wait again, this would be enough to prevent you from going > > > >I don't think polling is an acceptable solution to this problem. You > >user space code know needs to know what "idle" timeout you have > >selected so it can choose a faster poll rate. When is it safe to stop > >polling? > > I think the timeouts are of such an order of magnatude that the > polling can be infrequent enough to not be a significant amount of > load, but be faster than any timeout > > >>to sleep (or am I misunderstanding how long before you go into suspend > >>without a wakelock set, see my other e-mail for the full question) > >> > > > >We suspend as soon as no wakelocks are held. There is no delay. > > So, if I have a bookreader app that is not allowed to get the > wakelock, and nothing else is running, the system will suspend > immediatly after I click a button to go to the next page? it will > not stay awake to give me a chance to read the page at all? > > how can any application run without wakelock privilages? Isn't a wakelock held as long as the display is lit, so that the system would continue running as long as the page was visible? Thanx, Paul _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
