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Date:      Fri, 10 Nov 2006 14:24:34 -0800
From:      Jeremy Chadwick <freebsd@jdc.parodius.com>
To:        "Jason C. Wells" <jcw@highperformance.net>
Cc:        freebsd-stable <freebsd-stable@freebsd.org>
Subject:   Re: Compiler Options
Message-ID:  <20061110222434.GA76724@icarus.home.lan>
In-Reply-To: <4554D43E.5010700@highperformance.net>
References:  <4554D43E.5010700@highperformance.net>

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On Fri, Nov 10, 2006 at 11:34:22AM -0800, Jason C. Wells wrote:
> I have set CPUTYPE=p3 in make.conf.  When I compile my kernel I see 
> -march=pentium3 as I expect.  I also see -mno-mmx and -mno-sse are set 
> which I do not expect given that -march=pentium3 is used.  I presume 
> that I want MMX and SSE since my processor supports it.  What options do 
> I set and where do I set them to get a kernel properly tuned for pentium3?

The kernel will "support" MMX and SSE -- that is, any programs (root
or userland) which use MMX/SSE will work just fine.  That is: any
programs built with gcc can indeed support MMX and SSE operations.

The kernel itself _will not_ use any SSE or MMX operations when built.
This is because these optimisations are known to break the FreeBSD
kernel.  This applies to all i386 architectures, and probably 64-bit
architectures too (not sure).

CPUTYPE=p3 (or pentium4, or any other type) will not change this
behaviour.

-- 
| Jeremy Chadwick                                 jdc at parodius.com |
| Parodius Networking                        http://www.parodius.com/ |
| UNIX Systems Administrator                   Mountain View, CA, USA |
| Making life hard for others since 1977.               PGP: 4BD6C0CB |




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