On Fri, 28 May 2010 21:04:53 -0700 Arve Hjønnevåg <arve@xxxxxxxxxxx> wrote: > On Fri, May 28, 2010 at 7:52 PM, mark gross <640e9920@xxxxxxxxx> wrote: > > On Thu, May 27, 2010 at 05:23:54PM +1000, Neil Brown wrote: > >> On Wed, 26 May 2010 14:20:51 +0100 > >> Matthew Garrett <mjg59@xxxxxxxxxxxxx> wrote: > >> > >> > On Wed, May 26, 2010 at 02:57:45PM +0200, Peter Zijlstra wrote: > >> > > >> > > I fail to see why. In both cases the woken userspace will contact a > >> > > central governing task, either the kernel or the userspace suspend > >> > > manager, and inform it there is work to be done, and please don't > >> > > suspend now. > >> > > >> > Thinking about this, you're right - we don't have to wait, but that does > >> > result in another problem. Imagine we get two wakeup events > >> > approximately simultaneously. In the kernel-level universe the kernel > >> > knows when both have been handled. In the user-level universe, we may > >> > have one task schedule, bump the count, handle the event, drop the count > >> > and then we attempt a suspend again because the second event handler > >> > hasn't had an opportunity to run yet. We'll then attempt a suspend and > >> > immediately bounce back up. That's kind of wasteful, although it'd be > >> > somewhat mitigated by checking that right at the top of suspend entry > >> > and returning -EAGAIN or similar. > >> > > >> > >> (I'm coming a little late to this party, so excuse me if I say something that > >> has already been covered however...) > >> > >> The above triggers a sequence of thoughts which (When they settled down) look > >> a bit like this. > >> > >> At the hardware level, there is a thing that we could call a "suspend > >> blocker". It is an interrupt (presumably level-triggered) that causes the > >> processor to come out of suspend, or not to go into it. > >> > >> Maybe it makes sense to export a similar thing from the kernel to user-space. > >> When any event happens that would wake the device (and drivers need to know > >> about these already), it would present something to user-space to say that > >> the event happened. > >> > >> When user-space processes the event, it clears the event indicator. > > > > we did I proposed making the suspend enabling a oneshot type of thing > > and all sorts of weak arguments came spewing forth. I honestly couldn't > > tell if I was reading valid input or fanboy BS. > > > > Can you be more specific? If you are talking about only letting > drivers abort suspend, not block it, then the main argument against > that is that you are forcing user-space to poll until the driver stops > aborting suspend (which according to people arguing against us using > suspend would make the power-manager a "bad" process). Or are you > talking about blocking the request from user-space until all other > suspend-blockers have been released and then doing a single suspend > cycle before returning. This would not be as bad, but it would force > the user-space power manager to be multi-threaded since it now would > have way to cancel the request. Either way, what problem are you > trying to solve by making it a one-shot request? > I don't know exactly what Mark has in mind, but I would advocate 1-shot simply because what we currently have (echo mem > /sys/power/state) is 1-shot and I don't believe you need to do more than fix the bugs in that. Your question of whether to abort or block suspend in central I think - the answer to that question will make or break a possible solution. Simply aborting the suspend cannot work as you rightly say - the suspend daemon would then spin until other user-space processes get into action. Simply blocking while there are any unhandled 'wakeup events' - then aborting if there were any - is how I think it should work. However as it doesn't work that way now I don't think it is safe to make it work that way unconditionally. If we did we could find that existing configurations always block suspend indefinitely with would clearly be a regression. I think we still need some sort of "suspend_prepare". This would have two particular effects. 1/ it sets the start time for interpreting the word "were" above. i.e. the suspend would abort of there were any unhandled wakeup events since the "suspend_prepare" was issued. 2/ It would allow unhandled wakeup events to abort the suspend. If no suspend_prepare had been issued, then only "new" wakeup events would be allowed to abort the suspend (i.e. the old racy version of suspend). So the suspend daemon does: wait for there to be no user-space suspend blocks issue suspend_prepare check there are still no suspend blocks if there are, loop (possibly issue suspend_abort if needed) issue suspend request loop processes that handle wakeup events would poll for event to be available request suspend-block consume event release suspend-block loop (where consuming the event would quite possibly cause some other suspend-block to become active - e.g. it might request that the display be unlocked which would block suspends for a time). NeilBrown _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
