Dear list members, I'm following: http://people.virginia.edu/~chg5w/page3/assets/MeasuringUnix.pdf And I'm trying to measure executing time of simple operations with RDTSC. See the code below: #include <stdio.h> #define CPU_THOUSAND_HZ 800000 typedef unsigned long long ticks; static __inline__ ticks getticks(void) { unsigned a, d; asm("cpuid"); asm volatile("rdtsc" : "=a" (a), "=d" (d)); return (((ticks)a) | (((ticks)d) << 32)); } void main() { ticks tickBegin, tickEnd; tickBegin = getticks(); // code to time tickEnd = getticks(); double time = (tickEnd-tickBegin)/CPU_THOUSAND_HZ; printf ("%Le\n", time); } How can the C code detects the correct value for CPU_THOUSAND_HZ? The problems I see are: - It is needed to collect the information for the CPU that will run the process. On Core i7 processors, different cores can run at different clock speed at same time. - If the clock changes during the execution of process, what should it do? When is the best time for collecting the clock speed? The authors of the paper are not sure about the effects of "asm("cpuid");" Does it ensure that the entire process will run on the same CPU, and will serialize it avoiding out of order execution by the CPU? Thank you very much! :-) Peter -- Peter Senna Tschudin peter.senna@xxxxxxxxx gpg id: 48274C36 _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
