SYSPAGE_ENTRY(qtime)->cycles_per_sec

I measure time differences using ClockCycles function and
SYSPAGE_ENTRY(qtime)->cycles_per_sec;

When I measure the same time difference with a high end GPS receiver I
measure a difference of about 1ms. Assuming that the clockcycles are correct
the SYSPAGE_ENTRY(qtime)->cycles_per_sec appears bogus.

Recomputing the frequency based on the GPS time results in a difference of
about 330kHz on a 850MHz P3.

How can I get a more precise value for the processor frequency?

Regards,

Marcus