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Date: Sun, 29 May 2005 11:29:43 -0700
From: Kris Kennaway <kris@obsecurity.org>
To: "Anthony M. Agelastos" <iqgrande@gmail.com>
Message-ID: <20050529182942.GB15632@xor.obsecurity.org>
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Cc: freebsd-questions@freebsd.org
Subject: Re: Kernel Optimizations Regarding SSE
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On Sun, May 29, 2005 at 10:48:20AM -0400, Anthony M. Agelastos wrote:
> Hello all,
>=20
> I am, as we converse, rebuilding world to 5-STABLE (from 5.4-STABLE 3 =20
> weeks ago). This is the first time that I am building a custom kernel =20
> and it only deviates from GENERIC in that I only have
>=20
> cpu         I686_CPU (without the I586 and I486 that were there from =20
> GENERIC)
>=20
> and I added
>=20
> option    CPU_ENABLE_SSE (per the Handbook's suggestion for Video =20
> Playback)
>=20
> That is it. In watching the compile of the new kernel, I notice that =20
> just about every cc command has the options:
>=20
> -mno-mmx -mno-3dnow -mno-sse -mno-sse2
>=20
> Is it me, or does those flags appear to be turning off the very thing =20
> I wanted turned on (to turn it on, wouldn't it be -mmmx -m3dnow -msse =20
> -msse2)?

You misunderstand what the option does.  It allows user code to use
SSE, it doesn't cause SSE to be magically used in the kernel.  Indeed,
this is not feasible; please search the mailing list archives for
extensive discussion of this issue.

Kris


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