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 -- Martin Burnicki Meinberg Funkuhren Bad Pyrmont Germany _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
