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.
thanks
-john
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