From owner-freebsd-questions  Tue May 15  1:40:19 2001
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To: dleimbac@earthlink.net
Cc: freebsd-questions@FreeBSD.ORG, arch@FreeBSD.ORG
Subject: Re: Gettimeofday Again... 
In-Reply-To: Your message of "Mon, 14 May 2001 22:39:32 CDT."
             <200105150337.UAA19677@gull.mail.pas.earthlink.net> 
Date: Tue, 15 May 2001 10:39:56 +0200
Message-ID: <30515.989915996@critter>
From: Poul-Henning Kamp <phk@critter.freebsd.dk>
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In message <200105150337.UAA19677@gull.mail.pas.earthlink.net>, dave writes:
>
>
>Well I have been on the IRC in and out of mail list archives and cannot get
>a good answer to this question...
>
>Why does gettimeofday perform so poorly on FreeBSD vs the same hardware on
>Linux 2.4.2?
>
>---SNIP-----
>#include <sys/time.h>
>#include <unistd.h>
>
>int main() {
> struct timeval tv1, tv2, tv3;
>
>  gettimeofday(&tv1, 0);
>  gettimeofday(&tv2, 0);
>  gettimeofday(&tv3, 0);
>
>  printf("Time 1 %d:%d\n", tv1.tv_sec, tv1.tv_usec);
>  printf("Time 2 %d:%d\n", tv3.tv_sec, tv3.tv_usec);
>
>}
>----SNIP-----
>
>I get anywhere from 14usec to 17usec just for the call to gettimeofday.
>
>On  the 2.4.2 linux kernel its something like 3usec.  
>
>I just want to know why we are so much slower.

Because we havn't particularly optimised it.  If we want to, we
can get to the point where a machine with a usable TSC doesn't
even have to enter the kernel.


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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