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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clock(3C)						   Standard C Library Functions 						 clock(3C)

NAME
clock - report CPU time used SYNOPSIS
#include <time.h> clock_t clock(void); DESCRIPTION
The clock() function returns the amount of CPU time (in microseconds) used since the first call to clock() in the calling process. The time reported is the sum of the user and system times of the calling process and its terminated child processes for which it has executed the wait(3C) function, the pclose(3C) function, or the system(3C) function. RETURN VALUES
Dividing the value returned by clock() by the constant CLOCKS_PER_SEC, defined in the <time.h> header, will give the time in seconds. If the process time used is not available or cannot be represented, clock returns the value (clock_t) -1. USAGE
The value returned by clock() is defined in microseconds for compatibility with systems that have CPU clocks with much higher resolution. Because of this, the value returned will wrap around after accumulating only 2147 seconds of CPU time (about 36 minutes). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
times(2), popen(3C), system(3C), wait(3C), attributes(5), standards(5) SunOS 5.11 24 Jul 2002 clock(3C)