On Wed, Jul 12, 2017 at 10:11 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > On Wed, 12 Jul 2017, dbasehore . wrote: >> On Wed, Jul 12, 2017 at 3:16 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: >> > There are more issues with this: If there is a hrtimer scheduled on that >> > last CPU which enters the idle freeze state and that timer is 10 minutes >> > away, then the check timer can't be programmed and the system will happily >> > stay for 10 minutes in some shallow C state without notice. Not really >> > useful. >> >> Are hrtimers not suspended after timekeeping_suspend is called? > > They are. As I said I forgot about the inner workings and that check for > state != shutdown confused me even more, as it just looked like this might > be a valid state. Okay. I'll add a comment to clarify this part. > >> > You know upfront whether the i915 power wells (or whatever other machinery) >> > is not powered off to allow the system to enter a specific power state. If >> > you think hard enough about creating infrastructure which allows you to >> > register power related facilities and then check them in that idle freeze >> > enter state, then you get immediate information WHY this happens and not >> > just the by chance notification about the fact that it happened. >> >> It's not always something that can be checked by software. There was >> one case where an ordering for powering down audio hardware prevented >> proper PC10 entry, but there didn't seem to be any way to check that. >> Hardware watchdogs also have the same lack of clarity, but most if not >> all desktop and mobile processors ship with one. Overall, this seems >> to be the best that can be done at this point in freeze, and we can't >> really rely on every part of the system properly validating it's state >> in its suspend operation. > > So if I understand correctly, this is the last resort of catching problems > which can't be detected upfront or are caused by a software bug. > > I'm fine with that, but please explain and document it proper. The current > explanation is confusing at best. Will do. > > Thanks, > > tglx
