On Wednesday 18 February 2009, Arve Hjønnevåg wrote: > On Tue, Feb 17, 2009 at 3:21 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > On Tuesday 17 February 2009, Alan Stern wrote: > >> On Tue, 17 Feb 2009, Rafael J. Wysocki wrote: > >> > >> > Phase 1: I agree that system-auto-suspend-on, system-auto-suspend-off would be > >> > useful, but I don't like the wakelocks interface. Do you think there is an > >> > alternative way/mechanism of doing this? > >> > >> I rather like the suggestions Matthew Garrett has been making. They > >> show how to improve the wakelock interface without losing any function. > >> > >> Really, the idea behind wakelocks comes down to the question of how to > >> determine when the system is sufficiently idle to go into auto-suspend. > >> There may be occasions when no task is runnable but userspace knows > >> that the system should not go to sleep because some work will be done > >> in the near future. (Arve's example of a non-empty input buffer is > >> such a case.) How should userspace let the kernel know whether it's > >> okay to suspend at these times? That is the problem userspace > >> wakelocks are meant to solve. > > > > Still, do we really need multiple user space wakelocks (I'd prefer to call them > > sleeplocks)? It seems that one such lock and a user space manager controlling > > it should be sufficient. > > Yes, we could have a user space manager that all userspace wakelocks > go through, but it would have to start before any other processes that > need wakelocks and it would need a blocking ipc mechanism. The > wakelock api that is provided to android applications does all this, > but it is only available to java code. Supporting multiple userspace > wakelocks in the kernel is simpler than adding another userspace > wakelock layer. > > >> Kernel wakelocks are a separate matter. They are more like a form of > >> optimization, preventing the kernel from starting an auto-suspend when > >> some driver knows beforehand that it will return -EBUSY. > > > > I think kernel-side autosuspend (or rather autosleep) should only happen > > after certain subset of devices have been suspended using a per-device > > run-time autosuspend mechanism. > > When the last wakelock is released the task that we woke up to perform > has finished. Why wait to re-enter suspend. I don't really understand this comment. Could you please explain a bit? > >> > Phase 3: Probably explicit control left to open/close. > >> > >> While that's generally a good idea, it's important to recognize that > >> some devices should be runtime-suspended even while they are open. > > > > From the kernel side, yes (and that should be transparent to the user space > > having them open). By the user space, no. > > Allowing user space to suspend input devices while they are still open > is useful. The user-space code that reads from the input devices does > not need to know if the device is suspended or not, and the kernel > cannot auto suspend input devices based on inactivity. Hmm. Why can't it? Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
