How to measure elapsed time under Windows?

Gabriel Genellina gagsl-py2 at yahoo.com.ar
Wed Feb 24 18:32:59 CET 2010


En Sat, 13 Feb 2010 17:29:45 -0300, Tim Roberts <timr at probo.com> escribió:
> "Gabriel Genellina" <gagsl-py2 at yahoo.com.ar> wrote:
>>
>> The original problem was with the RDTSC instruction on multicore CPUs;
>> different cores may yield different results because they're not
>> synchronized at all times.
>
> Not true.  The synchronization issue has two causes:  initial
> synchronization at boot time, and power management making microscopic
> adjustments to the clock rate.  In Windows NT 4, Microsoft took extra  
> pains
> to adjust the cycle counters on multiprocessor computers during boot so
> that the processors started out very close together.  Once set, they
> naturally remained in lock step, until aggressive power management  
> because
> more prevalent.  In XP, they stopped trying to align at boot time.

Thanks for the detailed explanation!

-- 
Gabriel Genellina




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