On Wed, Aug 04, 2010 at 03:56:42PM -0700, david@xxxxxxx wrote: > 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) The difference between the Android scheme and your proposal is that the Android scheme freezes -all- the processes, not just a subset of them. Therefore, in the Android scheme, the case of one process attempting to acquire a resource held by a frozen process. In contrast, any scheme that attempts to freeze only a subset of the processes must somehow either avoid or properly handle the situation where a frozen process is holding a resource that a running process is trying to acquire. Thanx, Paul _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
