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 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 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) David Lang _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
