* John Stultz <john.stu...@linaro.org> wrote:
> On 05/06/2013 11:53 PM, Ingo Molnar wrote:
> >* Feng Tang <feng.t...@intel.com> wrote:
> >
> >>>is even worse than that. Machine can stay is s2ram for weeks (for a
> >>>lot more if it is desktop and you do s2ram for powersaving). Also
> >>>temperature of CPU varies a lot between active and s2ram states. Is
> >>>TSC good enough?
> >>Yes, I think it is relatively precise. Per our test, system time backed
> >>by the S3 non stop TSC only has 1 second drift after 4 days running
> >>(with mixed running and S3 states). And before using this feature, we've
> >>seen many time drift problems due to the RTC HW or system FW with our
> >>platforms.
> >Nice result ...
> >
> >Is that with NTP running?
> >
> > Without NTP, the TSC fast-calibration on bootup is not (expected to
> > be) nearly as precise as the 1:345600 precision you've measured.
>
> We also do refined calibration now on the TSC asynchronously over a
> period of seconds at boot up that gives us much better accuracy then the
> fast calibration. This helps provide much more consistent boot-to-boot
> TSC frequencies.
Indeed, I just checked from the logs of a system booting newer kernels how
well it works in practice, and it's about 10 ppm or better, which is much
better than the ~1000 ppm calibration inaccuracy I remembered.
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
