Messages in this thread | | | Date | Tue, 7 May 2013 19:18:55 +0200 | From | Ingo Molnar <> | Subject | Re: Fwd: [GIT PULL] timer changes for v3.10 |
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* John Stultz <john.stultz@linaro.org> wrote:
> On 05/06/2013 11:53 PM, Ingo Molnar wrote: > >* Feng Tang <feng.tang@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
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