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SubjectRe: a faster way to gettimeofday?
On Tue, 5 Mar 2002, Ben Greear wrote:

>
>
> Davide Libenzi wrote:
>
> > On Tue, 5 Mar 2002, Ben Greear wrote:
> >
> >
> >>I have a program that I very often need to calculate the current
> >>time, with milisecond accuracy. I've been using gettimeofday(),
> >>but gprof shows it's taking a significant (10% or so) amount of
> >>time. Is there a faster (and perhaps less portable?) way to get
> >>the time information on x86? My program runs as root, so should
> >>have any permissions it needs to use some backdoor hack if that
> >>helps!
> >>
> >
> > If you're on x86 you can use collect rdtsc samples and convert them to ms.
> > You'll get even more then ms accuracy.
>
>
> Can I do this from user space? If so, any examples or docs
> you can point me to?
>
> Also, I'm looking primarily for a speed increase, not an accuracy
> increase.


#include <linux/timex.h>


unsigned long long mscurr;
cycles_t cys, cye, mscycles;
struct timespec ts1, ts2;

clock_gettime(CLOCK_REALTIME, &ts1);
cys = get_cycles();
sleep(1);
clock_gettime(CLOCK_REALTIME, &ts2);
cye = get_cycles();
mscycles = (cye - cys) / ((ts2.tv_sec - ts1.tv_sec) * 1000 +
(ts2.tv_nsec - ts1.tv_nsec) / 1000000);


mscurr = ts2.tv_sec * 1000 + ts2.tv_nsec * 1000000 + (get_cycles() - cye) / mscycles;




- Davide


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