From owner-freebsd-questions  Thu Mar  7  7:16:15 2002
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Date: Thu, 7 Mar 2002 16:12:15 +0100 (MET)
From: Paul Everlund <tdv94ped@cs.umu.se>
To: "Brian T.Schellenberger" <bts@babbleon.org>
Cc: Peter Leftwich <Hostmaster@Video2Video.Com>,
	Justin L Boss <jlboss@yahoo.com>,
	FreeBSD-Questions <freebsd-questions@FreeBSD.ORG>
Subject: Re: Performance 686 - 386
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On Thu, 7 Mar 2002, Brian T.Schellenberger wrote:

> On Thursday 07 March 2002 01:16 am, Peter Leftwich wrote:
> | In my /etc/defaults/make.conf file, the line for CPUTYPE is commented out.
> |
> | # Currently the following CPU types are recognised:
> | #   Intel x86 architecture:
> | #       (AMD CPUs)      k7 k6-2 k6 k5
> | #       (Intel CPUs)    p4 p3 p2 i686 i586/mmx i586 i486 i386
> | #   Alpha/AXP architecture: ev6 pca56 ev56 ev5 ev45 ev4
> | # [snip]compiled with processor-specific (or higher - see below)
> | optimization flags. # If in doubt, do not set CPUTYPE or CFLAGS to
> | non-default values. #CPUTYPE=i686
> | #NO_CPU_CFLAGS= true    # Don't add -march=<cpu> to CFLAGS automatically
> | #NO_CPU_COPTFLAGS=true  # Don't add -march=<cpu> to COPTFLAGS automatically
> |
> | Does this matter?  Or is this option/parameter obtained from the current
> | kernel or something...?
>
> No, it means that the option is defaulting to the "default default" (to 486,
> I think).
>
> |
> | FreeBSD san.rr.com 4.5-RELEASE FreeBSD 4.5-RELEASE #0: Mon Jan 28 14:31:56
> | GMT 2002     murray@builder.freebsdmall.com:/usr/src/sys/compile/GENERIC
> | i386 (On an AMD Athlon 600MHz, 512mb RAM)

Why not try to compile the same program, using various options, and then
execute them by:
% time prog
Then you can see if there's any difference for that particular program. To
notice any difference though it should be a program that make use of a lot
of I686 specific instructions. I guess an easy hello world program does
not show any significant difference in execution time. :-)

/Paul


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