On Tuesday 01 June 2010, Alan Stern wrote: > On Tue, 1 Jun 2010, Neil Brown wrote: > > > > As I said before, we generally can't prevent such things from happening, > > > because even if we handle the particular race described above, it still is > > > possible that the event will be "lost" if it arrives just a bit later (eg. > > > during a suspend-toggle switch). So the PRE_SUSPEND thing won't really > > > solve the entire problem while increasing complexity. > > > > > > > My freerunner has a single core so without CONFIG_PREEMPT it may be that > > > > there is no actual race-window - maybe the PRE_SUSPENDs will all run before a > > > > soft_irq thread has a chance to finish handling of the interrupt (my > > > > knowledge of these details is limits). But on a muilti-core device I think > > > > there would definitely be a race-window. > > > > > > Yes, there always will be a race window. The only thing we can do is to > > > narrow it, but we cannot really close it (at least not on a PC, but I'm not > > > really sure it can be closed at all). > > > > Well you are the expert so I assume you are right, but I would really like to > > understand why this is. > > > > I guess that if the event was delivered as an edge-triggered interrupt which > > the interrupt controller couldn't latch, then it might get lost. Is that > > what happens? > > You're barking up the wrong tree. If I understand correctly, Rafael is > saying that there's a race involving events which are not _wakeup_ > events. If a non-wakeup event arrives shortly before a suspend, it can > have its normal effect. If it arrives while a suspend is in progress, > its delivery may be delayed until the system resumes. And if it > arrives after the system is fully suspended, it may never be noticed at > all. > > With wakeup events the problem isn't so bad. Wakeup events are always > noticed, and if the system is designed properly they will either abort > a suspend-in-progress or else cause the system to resume as soon as the > suspend is complete. (Linux is not yet properly designed in this > sense.) > > Or maybe I'm misunderstanding also, and Rafael is saying that there's > a race involving events whose meaning changes depending on whether or > not the system is asleep. This is obviously true and clearly > unavoidable. In fact I was referring to both in different places. That's why what I said wasn't too clear, sorry about that. Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
