Messages in this thread | | | Date | Wed, 4 Aug 2010 16:23:43 -0700 (PDT) | From | david@lang ... | Subject | Re: Attempted summary of suspend-blockers LKML thread |
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On Wed, 4 Aug 2010, Arve Hj?nnev?g wrote:
> 2010/8/4 <david@lang.hm>: >> On Wed, 4 Aug 2010, Arve Hj?nnev?g wrote: >> >>> On Wed, Aug 4, 2010 at 3:31 PM, <david@lang.hm> 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?
David Lang | |