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Full Discussion: RDTSC use in C:
Top Forums Programming RDTSC use in C: Post 302241860 by calv on Tuesday 30th of September 2008 01:08:24 PM
Old 09-30-2008
rdtsc is not good for time measurement.

The problem is, that the CPU might throttle (with it does most of the time, when all processes are blocked), so a cpu clock might mean more time in that case. This is of course CPU and OS dependant.
 
CLOCK_GETCPUCLOCKID(3)					   BSD Library Functions Manual 				    CLOCK_GETCPUCLOCKID(3)

NAME
clock_getcpuclockid -- access a process CPU-time clock LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <time.h> int clock_getcpuclockid(pid_t pid, clockid_t *clock_id); DESCRIPTION
The clock_getcpuclockid() returns the clock ID of the CPU-time clock of the process specified by pid. If the process described by pid exists and the calling process has permission, the clock ID of this clock will be returned in clock_id. If pid is zero, the clock_getcpuclockid() function returns the clock ID of the CPU-time clock of the process making the call, in clock_id. RETURN VALUES
Upon successful completion, clock_getcpuclockid() returns zero; otherwise, an error number is returned to indicate the error. ERRORS
The clock_getcpuclockid() function will fail if: [EPERM] The requesting process does not have permission to access the CPU-time clock for the process. [ESRCH] No process can be found corresponding to the process specified by pid. SEE ALSO
clock_gettime(2) STANDARDS
The clock_getcpuclockid() function conform to IEEE Std 1003.1-2001 (``POSIX.1''). HISTORY
The clock_getcpuclockid() function first appeared in FreeBSD 10.0. AUTHORS
David Xu <davidxu@FreeBSD.org> BSD
August 21, 2012 BSD
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