Re: [RFC PATCH 0/5] Add support for S3 non-stop TSC support.

[Pavel Machek <pavel@ucw.cz>]

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
-- 
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