> >>> > >> Note that the accuracy of this depends on several factors, such as how > >> long the measured interval is compared to the basic unit of timekeeping > >> (IOW if you want to measure the execution time of a short sequence of > >> instructions, you need to loop a few million times and divide the > >> result), and how much overhead is incurred in calling the timing > >> routines. > > Btw, this webpage > > https://stackoverflow.com/questions/23847588/how-do-i-use-the-functions-setitimer-and-getitimer > > says that getitimer and setitimer are obsolete and I should be using > > timer_gettime() and timer_settime() instead: however, is it possible > > to handle a virtual clock with these new functions? > > > > Best wishes, > > Ranjan > > the manp ages for the posix compliant interfaces for timer_settime and > timer_gettime > do not even mention the word virtual; at least not in my fedora 22 manpages. > Whereas the still valid setitimer and getitimer CAN get the per running > process virtual time, > which will exclude all system time and interrupt handling time. > There are plenty of examples online for using setitimer() and getitimer(). > OK, trying an example: #include <sys/time.h> #include <stdlib.h> #include <stdio.h> #include <limits.h> #define INTERVAL 1 /* number of milliseconds to go off */ int main() { double sum = 0; struct itimerval initial, updated; initial.it_value.tv_sec = INTERVAL/1000000; initial.it_value.tv_usec = (INTERVAL/1000000) * 1000000; initial.it_interval = initial.it_value; if (setitimer(ITIMER_VIRTUAL, &initial, NULL) == -1) { perror("error calling setitimer()"); exit(1); } for (unsigned int i; i < UINT_MAX; i++) { sum += 1./i; } if (getitimer(ITIMER_VIRTUAL, &updated) == -1) { perror("error calling getitimer()"); exit(1); } printf("Time started = %ld\n; Time taken = %ld\n: Time taken = %ld\n", initial.it_value.tv_usec, updated.it_value.tv_usec, updated.it_value.tv_usec - initial.it_value.tv_usec); return 0; } compiled with: $ gcc -o timer -std=c99 -Wall -pedantic getitimer.c -lrt However: I always get zero. $ ./timer Time started = 0 ; Time taken = 0 : Time taken = 0 What am I doing wrong? Many thanks, Ranjan ____________________________________________________________ Can't remember your password? Do you need a strong and secure password? Use Password manager! It stores your passwords & protects your account. Check it out at http://mysecurelogon.com/manager -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
