On Thursday, August 05, 2010, Arve Hjønnevåg wrote: > On Wed, Aug 4, 2010 at 1:56 PM, Matthew Garrett <mjg59@xxxxxxxxxxxxx> 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 > > How? By passing a timeout to pm_wakeup_event when the network driver > gets the packet or by passing 0. If you pass a timeout it is the same > as using a wakelock with a timeout and should work (assuming the > timeout you picked is long enough). If you don't pass a timeout it > does not work, since the packet may not be visible to user-space yet. Alternatively, pm_stay_awake() / pm_relax() can be used. > > 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 > > I have seen no proposed way to use cgroups that will work. If you > leave some processes running while other processes are frozen you run > into problems when a frozen process holds a resource that a running > process needs. > > > > having this conversation? :) It'd be good to have some feedback from > > Google as to whether this satisfies their functional requirements. > > > > That is "this"? The merged code? If so, no it does not satisfy our > requirements. The in kernel api, while offering similar functionality > to the wakelock interface, does not use any handles which makes it > impossible to get reasonable stats (You don't know which pm_stay_awake > request pm_relax is reverting). Why is that a problem (out of curiosity)? > The proposed in user-space interface > of calling into every process that receives wakeup events before every > suspend call Well, you don't really need to do that. > is also not compatible with existing apps. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
