Re: a faster way to gettimeofday?

[Chris Friesen]

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!

#include <asm/msr.h>

/* get this value from the "cpu MHz" line of /proc/cpuinfo */
#define CLOCKSPEED xxxxxxxx

int main()
{
	unsigned int lowbegin, lowend, highbegin, highend;
	unsigned long long diff;
	double elapsed;

	rdtsc(lowbegin,highbegin);

	//do stuff

	rdtsc(lowend,highend);

	if (lowend < lowbegin)
		highend--;

	diff = (((unsigned long long) highend - highbegin) << 32) + (lowend -
lowbegin);

	elapsed = (double) diff / CLOCKSPEED;

	/* elapsed now has time in microseconds, do whatever you wantwith it */	
	
	return 0;
}

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