From owner-freebsd-questions  Tue Aug 29 17:47: 9 2000
Delivered-To: freebsd-questions@freebsd.org
Received: from femail4.sdc1.sfba.home.com (femail4.sdc1.sfba.home.com [24.0.95.84])
	by hub.freebsd.org (Postfix) with ESMTP id 3741C37B424
	for <questions@freebsd.org>; Tue, 29 Aug 2000 17:47:06 -0700 (PDT)
Received: from home.com ([24.12.186.185]) by femail4.sdc1.sfba.home.com
          (InterMail vM.4.01.03.00 201-229-121) with ESMTP
          id <20000830004619.VMNM8556.femail4.sdc1.sfba.home.com@home.com>;
          Tue, 29 Aug 2000 17:46:19 -0700
Message-ID: <39ABF71E.A3D8EF@home.com>
Date: Tue, 29 Aug 2000 17:47:10 +0000
From: rob <europax@home.com>
X-Mailer: Mozilla 4.74 [en] (X11; U; FreeBSD 4.1-STABLE i386)
X-Accept-Language: en
MIME-Version: 1.0
To: Mike Meyer <mwm@mired.org>
Cc: questions@freebsd.org
Subject: Re: CFLAGS -O, if I am running a 686, does it automatically target my 
 cpu?
References: <14764.5348.342064.352183@guru.mired.org>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: owner-freebsd-questions@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

Mike Meyer wrote:
> 
> rob writes:
> > I am curious about whether make automatically tells gcc to optimize to
> > my machine's cpu, a 686, or does it optimize to a 386?  Reading though
> > the manuals, I can see that gcc can target a 686 or any other cpu, but I
> > have no idea what happens when I use make to compile my system or a
> > port.   Rob.
> 
> I vaguely recall that it optimizes for the *family*. However, the
> interesting part is found in the -mcpu documentation:
> 
>         the  compiler  will  not
>         generate  any  code  that  does not run on the i386
>         without the -march=cpu type option being used.
> 
> So you're going to be running 386 instructions on your machine unless
> you set add a -march flag to the compile.
> 
> On FreeBSD, you can set these in /etc/make.conf. Use CFLAGS for ports
> and other userland code, and COPTFLAGS for the kernel.
> 
>         <mike


Mike,  thanks for the info.  I thought about this after I did make
world. Dohh! I wonder if optimizing for a 686 would have made any
noticable difference anyway.  

I am going to try an interesting experiment and see if the -march=cpu
option gives me a better mpg123 program.  The mp3 performance that I
have now is kind of marginal, but that may be due wholly to shared
interupts on this laptop.  Rob.


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-questions" in the body of the message