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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(P)					     POSIX Programmer's Manual					    CLOCK_GETCPUCLOCKID(P)

NAME
clock_getcpuclockid - access a process CPU-time clock (ADVANCED REALTIME) SYNOPSIS
#include <time.h> int clock_getcpuclockid(pid_t pid, clockid_t *clock_id); DESCRIPTION
The clock_getcpuclockid() function shall return 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 shall be returned in clock_id. If pid is zero, the clock_getcpuclockid() function shall return the clock ID of the CPU-time clock of the process making the call, in clock_id. The conditions under which one process has permission to obtain the CPU-time clock ID of other processes are implementation-defined. RETURN VALUE
Upon successful completion, clock_getcpuclockid() shall return zero; otherwise, an error number shall be returned to indicate the error. ERRORS
The clock_getcpuclockid() function shall fail if: EPERM The requesting process does not have permission to access the CPU-time clock for the process. The clock_getcpuclockid() function may fail if: ESRCH No process can be found corresponding to the process specified by pid. The following sections are informative. EXAMPLES
None. APPLICATION USAGE
The clock_getcpuclockid() function is part of the Process CPU-Time Clocks option and need not be provided on all implementations. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
clock_getres() , timer_create() , the Base Definitions volume of IEEE Std 1003.1-2001, <time.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE
/The Open Group 2003 CLOCK_GETCPUCLOCKID(P)
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