Evandro Menezes wrote: > On Jan 21, 10:42 am, Martin Burnicki <[email protected]> > wrote: >> Ah, that's interesting. I did know that new CPU cores may not suffer from >> switched CPU clocks anymore, but I didn't know this is because they are >> driven by the FSB clock. So I assume the QPC clock frequency reported by >> Windows can also correspond to the FSB clock. > > Only indirectly. You certainly know that the CPU clock is a multiple > of the FSB clock. The unit of the result returned by RDTSC is still > CPU clock ticks, always. So, when the CPU clock multiplier is changed > from, say, 3.5 to 1.0, due to a power management decision, the TSC > circuitry is changed accordingly, so that its unit is the same as the > CPU's. The result is that when measuring the CPU clock, one will > still get it right. > > However, the precision of the TSC is not 1 CPU clock tick anymore, but > the FSB multiplier. So it cannot be used so easily to measure how > many CPU clock cycles a sequence of instructions takes anymore. > AFAIK, on AMD processors it's still possible to chose between variant > and invariant TSC. But I think that the tendency is for BIOS makers > to not offer this option and just enable the invariant TSC, since only > developers care about its precision (and they can use a performance > counter for the same purpose). > > HTH
Yes, it helps indeed ;-) Interesting details I didn't know, yet. Thanks, Martin -- Martin Burnicki Meinberg Funkuhren Bad Pyrmont Germany _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
