Great!! thanks for the tar.
I'm not sure if we can time() sys call is quite expensive all time.
Simple code I tried
#include <stdio.h>
#include <time.h>
int main()
{
int i,k = 0;
time_t t,j;
for(i =0 ; i < 100; i++)
{
usleep(100);
//t = time(NULL);
k++;
//j = time(NULL);
}
}
Time without the time() calls.
time ./time_performance
real 0m2.091s
user 0m0.000s
sys 0m0.001s
output with time calls.
time ./time_performance
real 0m2.007s
user 0m0.000s
sys 0m0.001s
Almost same.
timing k++ is not the righ thing but the point is, time as such is not
so expensive IMHO. I did notice considerable difference when I loop to
a 100000 times without the usleep().
just k++ in the loop.
time ./time_performance
real 0m0.003s
user 0m0.000s
sys 0m0.003s
with time() sys call before and after k++ in the loop.
time ./time_performance
real 0m0.168s
user 0m0.026s
sys 0m0.139s
Cheers,
Vadi
On Thu, Jul 21, 2011 at 5:16 PM, Akos Marton <makos999@xxxxxxxxx> wrote:
> I advice you `man 3 clock`.
> If you want to get much more precision the attached project can help you.
> Does it help?
>
> Regards,
> mAkos
>
>
> Michal Nazarewicz wrote:
>> On Thu, 21 Jul 2011 06:41:14 +0200, Vadiraj <vadiraj.cs@xxxxxxxxx> wrote:
>>> I'm evaluating time consumed by method. I'm using time(NULL) system
>>> call to capture time before and after the call to the function.
>>> Just wanted to know if this has a considerable performance hit? For
>>> all I believe time syscall is quite optimized and should not really be
>>> matter of concern.
>>>
>>> Please let me know if someone have evaluated time(NULL) system over head..
>>>
>>> Assuming the method I'm evaluating is a frequently called method.
>>
>> Why do you worry about it? What do you need the time for? If are
>> really using time(2) it means that the function you're calling run time
>> is counted in seconds. If that's the case, two call to time(2) are
>> by all means negligible.
>>
>> If you need in for benchmark, you would probably do something like:
>>
>> start = time(NULL)
>> for (vary big number)
>> call function you benchmark
>> end = time(NULL)
>>
>> In either case, you should check gettimeofday(2).
>>
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
