On Sun, Jun 6, 2010 at 5:01 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Sun, 6 Jun 2010, Matthew Garrett wrote: > >> The difference between idle-based suspend and opportunistic suspend is >> that the former will continue to wake up for timers and will never be >> entered if something is using CPU, whereas the latter will be entered >> whenever no suspend blocks are held. The problem with opportunistic >> suspend is that you might make the decision to suspend simultaneusly >> with a wakeup event being received. Suspend blocks facilitate >> synchronisation between the kernel and userspace to ensure that all such >> events have been consumed and handld appropriately. > > Remember that suspend takes place in several phases, the first of which > is to freeze tasks. The phases can be controlled individually by the > process carrying out a suspend, and there's nothing to prevent you from > stopping after the freezer phase. Devices won't get powered down, but > Android uses aggressive runtime power management for its devices > anyway. > > If you do this then the synchronization can be carried out entirely > from userspace, with no need for kernel modifications such as suspend > blockers. And since Android can reach essentially the same low-power > state from idle as from suspend, it appears that they really don't need > any kernel changes at all. > I don't think this is true. If you stop after the freezer phase you still need all the suspend blockers that are held until user-space consumes an event, otherwise it never gets consumed since user-space is frozen. -- Arve Hjønnevåg _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
