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Date: Wed, 06 Mar 2002 11:16:08 -0500
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From: Chris Friesen <cfriesen@nortelnetworks.com>
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To: Ben Greear <greearb@candelatech.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: a faster way to gettimeofday?
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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;
}


-- 
Chris Friesen                    | MailStop: 043/33/F10  
Nortel Networks                  | work: (613) 765-0557
3500 Carling Avenue              | fax:  (613) 765-2986
Nepean, ON K2H 8E9 Canada        | email: cfriesen@nortelnetworks.com
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