Once we detected 50 consecutive ticks with lost ticks (and this is half of
the amount needed to trigger the fallback to a "sane" timesource), verify
the CPU frequency is in sync if cpufreq is used: sometimes the CPU frequency
changes behind the user's back, and then the TSC detects lost ticks. By a
call to cpufreq_get(), the frequency the TSC driver thinks the CPU is in
is updated to the actual frequency, in case these differ. Works really nice
on my notebook -- it's never falling back to a different timesource now, even
if I plug in the power cord.