Martin Burnicki wrote: > David J Taylor wrote: >> David J Taylor wrote: >> [] >>> On the Intel 6600 dual-core, 2.4GHz processor here, under XP, a >>> RDTSC takes about 4.2ns, and a OS call to timeGetTime takes about >>> 11.8ns. At least, they do if my measurement program is working >>> correctly.... >>> >>> Haven't checked QPC. >>> >>> Cheers, >>> David >> >> And QueryPerformanceCounter takes some 226ns. Oh dear! > > Please keep in mind the QPC function also *tries* to handle the CPU > specific stuff consistent, if I understand the docs correctly. > > From the Microsoft SDK: > "On a multiprocessor computer, it should not matter which processor is > called. However, you can get different results on different > processors due to bugs in the basic input/output system (BIOS) or the > hardware abstraction layer (HAL)." > > The latter is obviously the case with some AMD CPUs. > > Anyway, if your code uses RDTSC directly insrtead of QPC then *your > code* may have to take care about this, and you have to take this > also into account if you compare execution times. > > Of course I know you can limit these problems using explicite CPU > affinity. > > Martin
Thanks, Martin. I was simply reprting the speeds I found, rather than attempting to make any comment on which you should call or why. Cheers, David _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions