[ntp:questions] Timekeeping broken on Windows XP with multimedia timer enabled (-M option)

Evandro Menezes evandro at mailinator.com
Thu Jan 21 15:53:45 UTC 2010

On Jan 21, 4:43 am, Martin Burnicki <martin.burni... at meinberg.de>
> AFAIK this should only affect the TSCs, so the setting should not matter at
> all if the PM timer is used.

Another detail on RDTSC: newer cores, such as Intel's Core2 and AMD's
Phenom, return a constant-rate readout by RDTSC.  In actuality, the
counter that RDTSC is driven by the FSB clock instead of by the CPU
clock and, even if the later changes due to power management, it's
adjusted accordingly.

But it all boils down to the HAL, which will use whatever's necessary
to make sure that what QueryPerformanceCounter returns is independent
of the CPU clock.


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