Rob Williscroft wrote: > Claudio Grondi wrote in news:[EMAIL PROTECTED] in > gmane.comp.python.general: > > >>Tim Roberts wrote: >> >>>"Tim Peters" <[EMAIL PROTECTED]> wrote: > > >>>It is much simpler than that. With a multiprocessor HAL, including >>>on a dual-core or hyperthreaded system, QueryPerformanceCounter >>>returns the raw cycle counter (RDTSC). However, on Windows XP, the >>>operating system does not synchronize the cycle counters on multiple >>>processors, and they can be actually be millions of cycles apart. >>> >>>This was a change from previous systems. On NT4 and Win2000, the >>>operating actually rewrote the cycle counters on the second (and >>>beyond) processors to align them to the first processor, so the delta >>>was usually only a dozen or two cycles. XP does not appear to do >>>that. I think that is a huge mistake, since it renders >>>QueryPerformanceCounter non-monotonic. >> >>How does it come, that processors on same mainboard run at different >>speeds? Do they have separate clock-pulse generators? > > > I don't see any claim above that they run at different speeds, only > that the counters are several million cycles apart, IOW running at the > same speed but with different initial values, or more likely starting > at different times. > > For processors that run at (say) 2GHz, several million (say 10 million) > represents a difference of 10e6/2e9 = 0.005 seconds between when the > processors were sufficiently powered up to start counting cycles. > > Rob.
If it were so, than why can't the delta of time between the processors be set to exact zero? I assume, that it is known how many cycles adjusting the value will take, so it could be done exactly ... hmmm ... Claudio Grondi -- http://mail.python.org/mailman/listinfo/python-list