ı need to calculate how many nanosecond the process takes . must give the same value every time (c++)
ubuntu 10.10
my system information------------------------------------------------------
*-cpu
description: CPU
product: Intel(R) Core(TM)2 Duo CPU T7300 @ 2.00GHz
vendor: Intel Corp.
physical id: 400
bus info: cpu@0
slot: Microprocessor
size: 2001MHz
capacity: 2001MHz
width: 64 bits
clock: 200MHz
*-cache:0
description: L1 cache
physical id: 700
size: 32KiB
capacity: 32KiB
capabilities: internal write-back data
*-cache:1
description: L2 cache
physical id: 701
size: 4MiB
capacity: 4MiB
clock: 66MHz (15.0ns)
capabilities: pipeline-burst internal varies unified
*-memory
description: System Memory
physical id: 1000
slot: System board or motherboard
size: 4GiB
*-bank:0
description: DIMM DDR Synchronous 667 MHz (1.5 ns)
product: 9905295-051.A00LF
vendor: Kingston
physical id: 0
serial: 53CC4D13
slot: DIMM_A
size: 2GiB
width: 64 bits
clock: 667MHz (1.5ns)
*-bank:1
description: DIMM DDR Synchronous 667 MHz (1.5 ns)
product: 9905295-051.A00LF
vendor: Kingston
physical id: 1
serial: 51CC4E13
slot: DIMM_B
size: 2GiB
width: 64 bits
clock: 667MHz (1.5ns)

Code-----------------------------------------------------------------------
#include <stdio.h>
#include <time.h>

int main ()
{
struct timespec t1;
struct timespec t2;

clock_gettime(CLOCK_REALTIME, &t1);
clock_gettime(CLOCK_REALTIME, &t2);
printf ("CLOCK_REALTIME : %ld\n", t2.tv_nsec-t1.tv_nsec );

clock_gettime(CLOCK_MONOTONIC, &t1);
clock_gettime(CLOCK_MONOTONIC, &t2);
printf ("CLOCK_MONOTONIC : %ld\n", t2.tv_nsec-t1.tv_nsec );

clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &t1);
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &t2);
printf ("CLOCK_PROCESS_CPUTIME_ID : %ld\n", t2.tv_nsec-t1.tv_nsec );

clock_gettime(CLOCK_THREAD_CPUTIME_ID, &t1);
clock_gettime(CLOCK_THREAD_CPUTIME_ID, &t2);
printf ("CLOCK_THREAD_CPUTIME_ID : %ld\n", t2.tv_nsec-t1.tv_nsec );

}
-----------------------------------------------------------------
compile use -lrt
"gcc -lrt example.c -o example"

first result ----------------------------------------------------
CLOCK_REALTIME : 1118
CLOCK_MONOTONIC : 1187
CLOCK_PROCESS_CPUTIME_ID : 736
CLOCK_THREAD_CPUTIME_ID : 396

second result
CLOCK_REALTIME : 1187
CLOCK_MONOTONIC : 1117
CLOCK_PROCESS_CPUTIME_ID : 647
CLOCK_THREAD_CPUTIME_ID : 411

Hi, welcome to LQ!

Find an OS that runs your program as its only task.




Cheers,
Tink

I am with Tink on this one. If you can guarantee no other tasks will take any of the cpu, ram or disk time away from your task then "maybe"
you will get the same times or perhaps close. Especially when measuring at such a low level.

you could record the times and MAYBE do a normal distribution, so you can draw a conclusion like with a mean 530 sd 50, 600 lies above 80% or something. IF you really want a statistical analysis. But its impossible to give a exact consistency even to seconds.
Ted

end

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who know not multi-thread linux version

Was there something you are trying to say? No amount of data based on your machine features will help this scenario.
You can try to include the timings of all things running on your machine, but of course then the issue is what does the scheduler in
the cpu choose to give priority to?? As has been mentioned by a few people now, depending on what is running on your system whilst executing
your code will affect the timings, even if only slightly.