[PATCH 0/8] Suspend block api (version 8)
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From: Arve Hjønnevåg on 2 Jun 2010 00:50 2010/6/1 James Bottomley <James.Bottomley(a)suse.de>: > On Tue, 2010-06-01 at 18:10 -0700, Arve Hj�nnev�g wrote: >> On Tue, Jun 1, 2010 at 3:36 PM, James Bottomley <James.Bottomley(a)suse.de> wrote: >> > On Wed, 2010-06-02 at 00:24 +0200, Rafael J. Wysocki wrote: >> >> On Tuesday 01 June 2010, James Bottomley wrote: >> >> > On Tue, 2010-06-01 at 14:51 +0100, Matthew Garrett wrote: >> >> > > On Mon, May 31, 2010 at 04:21:09PM -0500, James Bottomley wrote: >> >> > > >> >> > > > You're the one mentioning x86, not me. �I already explained that some >> >> > > > MSM hardware (the G1 for example) has lower power consumption in S3 >> >> > > > (which I'm using as an ACPI shorthand for suspend to ram) than any >> >> > > > suspend from idle C state. �The fact that current x86 hardware has the >> >> > > > same problem may be true, but it's not entirely relevant. >> >> > > >> >> > > As long as you can set a wakeup timer, an S state is just a C state with >> >> > > side effects. The significant one is that entering an S state stops the >> >> > > process scheduler and any in-kernel timers. I don't think Google care at >> >> > > all about whether suspend is entered through an explicit transition or >> >> > > something hooked into cpuidle - the relevant issue is that they want to >> >> > > be able to express a set of constraints that lets them control whether >> >> > > or not the scheduler keeps on scheduling, and which doesn't let them >> >> > > lose wakeup events in the process. >> >> > >> >> > Exactly, so my understanding of where we currently are is: >> >> >> >> Thanks for the recap. >> >> >> >> > � � �1. pm_qos will be updated to be able to express the android suspend >> >> > � � � � blockers as interactivity constraints (exact name TBD, but >> >> > � � � � probably /dev/cpu_interactivity) >> >> >> >> I think that's not been decided yet precisely enough. �I saw a few ideas >> >> here and there in the thread, but which of them are we going to follow? >> > >> > Well, android only needs two states (block and don't block), so that >> > gets translated as 2 s32 values (say 0 and INT_MAX). �I've seen defines >> > like QOS_INTERACTIVE and QOS_NONE (or QOS_DRECKLY or QOS_MANANA) to >> > describe these, but if all we're arguing over is the define name, that's >> > progress. >> >> I think we need separate state constraints for suspend and idle low >> power modes. On the msm platform only a subset of the interrupts can >> wake up from the low power mode, so we block the use if the low power >> mode from idle while other interrupts are enabled. We do not block >> suspend however if those interrupts are not marked as wakeup >> interrupts. Most constraints that prevent suspend are not hardware >> specific and should not prevent entering low power modes from idle. In >> other words we may need to prevent low power idle modes while allowing >> suspend, and we may need to prevent suspend while allowing low power >> idle modes. > > Well, as I said, pm_qos is s32 ... it's easy to make the constraint > ternary instead of binary. No, they have to be two separate constraints, otherwise a constraint to block suspend would override a constraint to block a low power idle mode or the other way around. > >> It would also be good to not have an implementation that gets slower >> and slower the more clients you have. With binary constraints this is >> trivial. > > Well, that's an implementation detail ... ordering the list or using a True. I think we also need timeout support in the short term though which is also somewhat simpler to implement in an efficient way for binary constraints. > btree would significantly fix that. �However, the most number of > constraint users I've seen in android is around 60 ... that's not huge > from a kernel linear list perspective, so is this really a concern? ... > particularly when most uses don't necessarily change the constrain, so a > list search isn't done. The search is done every time any of them changes. > >> > The other piece they need is the suspend block name, which comes with >> > the stats API, and finally we need to decide what the actual constraint >> > is called (which is how the dev node gets its name) ... >> > >> >> > � � �2. pm_qos will be updated to be callable from atomic context >> >> > � � �3. pm_qos will be updated to export statistics initially closely >> >> > � � � � matching what suspend blockers provides (simple update of the rw >> >> > � � � � interface?) >> >> 4. It would be useful to change pm_qos_add_request to not allocate >> anything so can add constraints from init functions that currently >> cannot fail. > > Sure .. we do that for the delayed work queues, it's just an API which > takes the structure as an argument leaving it the responsibility of the > caller to free. > >> >> > After this is done, the current android suspend block patch becomes a >> >> > re-expression in kernel space in terms of pm_qos, with the current >> >> > userspace wakelocks being adapted by the android framework into pm_qos >> >> > requirements expressed to /dev/cpu_interactivity (or whatever name is >> >> > chosen). �Then opportunistic suspend is either a small add-on kernel >> >> > patch they have in their tree to suspend when the interactivity >> >> > constraint goes to NONE, or it could be done entirely by a userspace >> >> > process. �Long term this could migrate to the freezer and suspend from >> >> > idle approach as the various problem timers get fixed. >> >> > >> >> > I think the big unresolved issue is the stats extension. �For android, >> >> > we need just a name written along with the value, so we have something >> >> > to hang the stats off ... current pm_qos userspace users just write a >> >> > value, so the name would be optional. �From the kernel, we probably just >> >> > need an additional API that takes a stats name or NULL if none >> >> > (pm_qos_add_request_named()?). �Then reading the stats could be done by >> >> > implementing a fops read routine on the misc device. >> >> >> >> Is the original idea of having that information in debugfs objectionable? >> > >> > Well ... debugfs is usually used to get around the sysfs rules. �In this >> > case, pm_qos has a dev interface ... I don't specifically object to >> > using debugfs, but I don't see any reason to forbid it from being a >> > simple dev read interface either. >> > >> >> We don't currently have a dev interface for stats so this is not an >> immediate requirement. The suspend blocker debugfs interface is just >> as good as the proc interface we have for wakelocks. > > OK, great ... what actually exports the statistics is just an > implementation detail. > > James > > > > -- Arve Hj�nnev�g -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Thomas Gleixner on 2 Jun 2010 03:10 On Tue, 1 Jun 2010, Arve Hj�nnev�g wrote: > 2010/6/1 Thomas Gleixner <tglx(a)linutronix.de>: > > > > On Mon, 31 May 2010, Arve Hj�nnev�g wrote: > > > >> On Mon, May 31, 2010 at 2:46 PM, Thomas Gleixner <tglx(a)linutronix.de> wrote: > >> > On Mon, 31 May 2010, James Bottomley wrote: > >> >> > >> >> For MSM hardware, it looks possible to unify the S and C states by doing > >> >> suspend to ram from idle but I'm not sure how much work that is. > >> > > >> > On ARM, it's not rocket science and we have in tree support for this > >> > already (OMAP). I have done the same thing on a Samsung part as a > >> > prove of concept two years ago and it's really easy as the hardware is > >> > sane. Hint: It's designed for mobile devices :) > >> > > >> > >> We already enter the same power state from idle and suspend on msm. In > >> the absence of misbehaving apps, the difference in power consumption > >> is entirely caused by periodic timers in the user-space framework > >> _and_ kernel. It only takes a few timers triggering per second (I > >> think 3 if they do no work) to double the average power consumption on > >> the G1 if the radio is off. We originally added wakelocks because the > >> hardware we had at the time had much lower power consumption in > >> suspend then idle, but we still use suspend because it saves power. > > > > So how do you differentiate between timers which _should_ fire and > > those you do not care about ? > > > > Only alarms are allowed to fire while suspended. > > > We have mechanisms in place to defer timers so the wakeups are > > minimized. If that's not enough we need to revisit. > > > > Deferring the the timers forever without stopping the clock can cause > problems. Our user space code has a lot of timeouts that will trigger > an error if an app does not respond in time. Freezing everything and > stopping the clock while suspended is a lot simpler than trying to > stop individual timers and processes from running. And resume updates timekeeping to account for the slept time. So the only way to get away with that is to sleep under a second or just ignoring the update by avoiding the access to rtc. So how do you keep timekeeping happy ? Thanks, tglx
From: Arve Hjønnevåg on 2 Jun 2010 03:20 2010/6/2 Thomas Gleixner <tglx(a)linutronix.de>: > On Tue, 1 Jun 2010, Arve Hj�nnev�g wrote: >> 2010/6/1 Thomas Gleixner <tglx(a)linutronix.de>: >> > >> > On Mon, 31 May 2010, Arve Hj�nnev�g wrote: >> > >> >> On Mon, May 31, 2010 at 2:46 PM, Thomas Gleixner <tglx(a)linutronix.de> wrote: >> >> > On Mon, 31 May 2010, James Bottomley wrote: >> >> >> >> >> >> For MSM hardware, it looks possible to unify the S and C states by doing >> >> >> suspend to ram from idle but I'm not sure how much work that is. >> >> > >> >> > On ARM, it's not rocket science and we have in tree support for this >> >> > already (OMAP). I have done the same thing on a Samsung part as a >> >> > prove of concept two years ago and it's really easy as the hardware is >> >> > sane. Hint: It's designed for mobile devices :) >> >> > >> >> >> >> We already enter the same power state from idle and suspend on msm. In >> >> the absence of misbehaving apps, the difference in power consumption >> >> is entirely caused by periodic timers in the user-space framework >> >> _and_ kernel. It only takes a few timers triggering per second (I >> >> think 3 if they do no work) to double the average power consumption on >> >> the G1 if the radio is off. We originally added wakelocks because the >> >> hardware we had at the time had much lower power consumption in >> >> suspend then idle, but we still use suspend because it saves power. >> > >> > So how do you differentiate between timers which _should_ fire and >> > those you do not care about ? >> > >> >> Only alarms are allowed to fire while suspended. >> >> > We have mechanisms in place to defer timers so the wakeups are >> > minimized. If that's not enough we need to revisit. >> > >> >> Deferring the the timers forever without stopping the clock can cause >> problems. Our user space code has a lot of timeouts that will trigger >> an error if an app does not respond in time. Freezing everything and >> stopping the clock while suspended is a lot simpler than trying to >> stop individual timers and processes from running. > > And resume updates timekeeping to account for the slept time. So the No, for the monotonic clock it does the opposite. The hardware clock is read on resume and the offset is set so the monotonic clock gets the same value as it had when suspend was called. > only way to get away with that is to sleep under a second or just > ignoring the update by avoiding the access to rtc. > > So how do you keep timekeeping happy ? > -- Arve Hj�nnev�g -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Thomas Gleixner on 2 Jun 2010 03:30 On Wed, 2 Jun 2010, Arve Hj�nnev�g wrote: > 2010/6/2 Thomas Gleixner <tglx(a)linutronix.de>: > > On Tue, 1 Jun 2010, Arve Hj�nnev�g wrote: > >> Deferring the the timers forever without stopping the clock can cause > >> problems. Our user space code has a lot of timeouts that will trigger > >> an error if an app does not respond in time. Freezing everything and > >> stopping the clock while suspended is a lot simpler than trying to > >> stop individual timers and processes from running. > > > > And resume updates timekeeping to account for the slept time. So the > > No, for the monotonic clock it does the opposite. The hardware clock > is read on resume and the offset is set so the monotonic clock gets > the same value as it had when suspend was called. Grr, yes. Misread the code. -ENOTENOUGHCOFFEE Thanks, tglx
From: Thomas Gleixner on 2 Jun 2010 04:40
On Tue, 1 Jun 2010, Arve Hj�nnev�g wrote: > 2010/6/1 Thomas Gleixner <tglx(a)linutronix.de>: > > On Mon, 31 May 2010, Arve Hj�nnev�g wrote: > > > >> 2010/5/31 Rafael J. Wysocki <rjw(a)sisk.pl>: > >> > On Monday 31 May 2010, Arve Hj�nnev�g wrote: > >> >> 2010/5/30 Rafael J. Wysocki <rjw(a)sisk.pl>: > >> > ... > >> >> > >> >> I think it makes more sense to block suspend while wakeup events are > >> >> pending than blocking it everywhere timers are used by code that could > >> >> be called while handling wakeup events or other critical work. Also, > >> >> even if you did block suspend everywhere timers where used you still > >> >> have the race where a wakeup interrupt happens right after you decided > >> >> to suspend. In other words, you still need to block suspend in all the > >> >> same places as with the current opportunistic suspend code, so what is > >> >> the benefit of delaying suspend until idle? > >> > > >> > Assume for a while that you don't use suspend blockers, OK? �I realize you > >> > think that anything else doesn't make sense, but evidently some other people > >> > have that opinion about suspend blockers. > >> > > >> > >> It sounded like you were suggesting that initiating suspend from idle > >> would somehow avoid the race condition with wakeup events. All I'm > >> saying is that you would need to block suspend in all the same places. > >> If you don't care about ignoring wakeup events, then sure you can > >> initiate suspend from idle. > > > > And why should you miss a wakeup there ? If you get an interrupt in > > the transition, then you are not longer idle. > > > > Because suspend itself causes you to not be idle you cannot abort > suspend just because you are not idle anymore. You still are addicted to the current suspend mechanism. :) The whole point of doing it from idle in the form of a deep power state is to avoid the massive sh*tload of work which is neccesary to run the existing suspend code. But that needs runtime power management and tweaks to avoid your timers waking you, etc. The mechanism you want to use is: suspend no matter what, like closing the lid of the laptop, but with a few tweaks around it: 1) An interrupt on a wakeup source which comes in while the suspend code runs, i.e before you transitioned into wakeup mode, must abort / prevent suspend. 2) Prevent another attempt to suspend before the event has been delivered and the apps have signaled that they have not longer any work to do. As a side effect you confine crappy apps with that mechanism in some way. In the laptop case we do not want the tweaks as not going into suspend might set your backpack on fire. If I understood you correctly then you can shutdown the CPU in idle completelty already, but that's not enough due to: 1) crappy applications keeping the cpu away from idle 2) timers firing Would solving those two issues be sufficient for you or am I missing something ? Thanks, tglx |