On Sun, May 30, 2010 at 06:08:46PM +1000, Neil Brown wrote: > 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? > > Sorry about missing Avr's email, I've been fighting with getting my email forwarding working right. The problems I want to solve with the one-shot styled interface are: 1) of having to sprinkle suspend blocking sections from isr up to usermode and get them right. 2) provide a platform / architecture independent framework supporting other low power modes. I've just posted a patch that expresses what I was trying to express. Its hard to take design over email without tossing code back and forth. It's my turn to toss some code. > > Simply aborting the suspend cannot work as you rightly say - the suspend > daemon would then spin until other user-space processes get into action. Not if you have sensible event messaging to the user-space processes. I've posted a patch that attempts to add some messaging. > 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 In my mind I'm thinking of something like: attempt low power entry (suspend) if blocked, get -EBUSY back select on block_file until block is released retry suspend else // entered low power and exited read wake_event do something with event; typically wait a bit and loop. --mgross > > (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
