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CPU time on multitask applications

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Old 04-17-2008
CPU time on multitask applications
Hello all,

I'm using clock() function (from ctime) to realize how long it takes my threaded application to complete an algorithm. I would like to know how this function behaves in multicore boxes, that is: does it return the sum of the clock ticks of each processor the program was runned on ?
I'm asking this because I've splitted one single process into two threads, each of them performing half of the job, but I get that the execution time calculated through clock () is just the same that the one I get using the single-threaded version.

Thank you so much,
bye !
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LEARN ABOUT FREEBSD

clock_getcpuclockid

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