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. -- Arve Hjønnevåg _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
