Messages in this thread | | | Date | Mon, 1 Apr 2013 22:31:36 +0200 | From | Pavel Machek <> | Subject | Re: [RFC PATCH 0/5] Add support for S3 non-stop TSC support. |
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Hi!
> >>>On some new Intel Atom processors (Penwell and Cloverview), there is > >>>a feature that the TSC won't stop S3, say the TSC value won't be > >>>reset to 0 after resume. This feature makes TSC a more reliable > >>>clocksource and could benefit the timekeeping code during system > >>>suspend/resume cycles. > >>> > >>>The enabling efforts include adding new flags for this feature, > >>>modifying clocksource.c and timekeeping.c to support and utilizing > >>>it. > >>> > >>>One remaining question is inside the timekeeping_resume(), we don't > >>>know if it is called by resuming from suspend(s2ram) or from > >>>hibernate(s2disk), as there is no easy way to check it currently. > >>>But it doesn't hurt as these Penwell/Cloverview platforms only have > >>>S3 state, and no S4. > >>> > >>>Please help to review them, thanks! > >>The patches look reasonable to me. > >Not sure... what are advantages? TSC is high resolution, but not > >exactly precise time source... and this only makes resume more > >complex. > Providing sub-second granularity for suspend time measurement is a > pretty compelling use, which greatly reduces time error across > suspend/resume.
Certainly for short sleeps. Is TSC actually precise enough to keep precise time for hours? I thought TSC sucked at precision.
> I agree that the code logic is more complex, but the TSC path should > be a good bit faster then hitting the CMOS.
You are right here.
> There is the open concern that given their history, x86 designers > will find yet another way to break the TSC in some future chip and > we'll end up with non-stop TSCs that run at different frequencies in > suspend or some other such nonsense. But we'll just have to detect > that and disable functionality where appropriate, much as we do with > the TSC now.
Ok. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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