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SubjectRe: [patch 13/19] GTOD: Mark TSC unusable for highres timers
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	current_tsc_khz = tsc_khz;
> > clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
> > clocksource_tsc.shift);
> > +#ifndef CONFIG_HIGH_RES_TIMERS
> > /* lower the rating if we already know its unstable: */
> > if (check_tsc_unstable())
> > clocksource_tsc.rating = 0;
> > -
> > +#else
> > + /*
> > + * Mark TSC unsuitable for high resolution timers. TSC has so
> > + * many pitfalls: frequency changes, stop in idle ... When we
> > + * switch to high resolution mode we can not longer detect a
> > + * firmware caused frequency change, as the emulated tick uses
> > + * TSC as reference. This results in a circular dependency.
> > + * Switch only to high resolution mode, if pm_timer or such
> > + * is available.
> > + */
> > + clocksource_tsc.rating = 50;
> > + clocksource_tsc.is_continuous = 0;
> > +#endif
> > init_timer(&verify_tsc_freq_timer);
> > verify_tsc_freq_timer.function = verify_tsc_freq;
> > verify_tsc_freq_timer.expires =
>
>
> Hmmm. I wish this patch was unnecessary, but I don't see an easy
> solution.

Very sad. This will make a lot of people unhappy, even to the point
where they might prefer disabling noidlehz over super slow gettimeofday.
I assume you at least have a suitable command line option for that, right?

Can we get a summary on which systems the TSC is considered unstable?
Normally we assume if it's stable enough for gettimeofday it should
be stable enough for longer delays too.

-Andi

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