Re: a faster way to gettimeofday?

[Davide Libenzi]

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