On Sun, May 30, 2010 at 1:32 PM, mark gross <640e9920@xxxxxxxxx> wrote: > 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. Making the interface one-shot does not change where you need to block suspend. > > 2) provide a platform / architecture independent framework supporting > other low power modes. > I assume you did not mean that a one-shot interface has any impact on this. What other low power modes are you trying to support. Suspend blocker block suspend regardless of the mode selected (standby/mem). Are there cases where you need to block one but not the other? -- Arve Hjønnevåg _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
