[ntp:questions] micro-optimization

Augustine evandro at mailinator.com
Sat Mar 14 21:00:30 UTC 2009

On Mar 12, 3:59 am, Martin Burnicki <martin.burni... at meinberg.de>
> Do you have some pointers where this is explained?

Perhaps, suffice to look at page 252 and 293 of
where you can find the formula to calculate the latency for RDTSC on
Phenom processors.  Also page B-5 of http://download.intel.com/design/processor/manuals/248966.pdf,
where it states that the precision of RDTSC on Intel processors is 64
CPU clock cycles, and page C-29, where the latency is shown.

In both documents, several events that may cause the TSC to get out of
sync with time are also mentioned.  That's why the TSC has been
abandoned as a time source in recent kernels in favor of the PM timer
and HPET or even the PIT.


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