Date: Sat, 11 Nov 2006 02:30:51 +0100 From: Joerg Pernfuss <elessar@bsdforen.de> To: freebsd-stable@freebsd.org Cc: "Jason C. Wells" <jcw@highperformance.net>, Jeremy Chadwick <freebsd@jdc.parodius.com> Subject: Re: Compiler Options Message-ID: <20061111023051.38dbaa37@loki.starkstrom.lan> In-Reply-To: <200611111019.43944.doconnor@gsoft.com.au> References: <4554D43E.5010700@highperformance.net> <20061110222434.GA76724@icarus.home.lan> <200611111019.43944.doconnor@gsoft.com.au>
next in thread | previous in thread | raw e-mail | index | archive | help
--Sig_04Vhn.2bNPaHYz9VOtlqoSB Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Sat, 11 Nov 2006 10:19:42 +1030 "Daniel O'Connor" <doconnor@gsoft.com.au> wrote: > On Saturday 11 November 2006 08:54, Jeremy Chadwick wrote: > > 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). >=20 > I think this is mainly because the kernel has no FPU context so you > can't actually use any FPU operation (including SSE & MMX) without > potentially trashing userland data. If I remember correctly, this was the reason why some improvements from DragonFlyBSD were not ported to FreeBSD (or were ported but not committed). There was no conclusive evidence that the speed improvement for some operations would result in a net gain, due to register saving/restoring overhead during context switches. > (I could be wrong but the above is what I remember reading on various > lists over the years :) I think you remember right. Or I remember wrong too :) Joerg --=20 | /"\ ASCII ribbon | GnuPG Key ID | e86d b753 3deb e749 6c3a | | \ / campaign against | 0xbbcaad24 | 5706 1f7d 6cfd bbca ad24 | | X HTML in email | .the next sentence is true. | | / \ and news | .the previous sentence was a lie. | --Sig_04Vhn.2bNPaHYz9VOtlqoSB Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2.2 (FreeBSD) iD8DBQFFVSfLH31s/bvKrSQRAqsuAJ9HgCHBNXadTC+qOC/Lhl7kUX58YwCfQu6i cTDVkYpk+w7blSEskTa6wXM= =t49V -----END PGP SIGNATURE----- --Sig_04Vhn.2bNPaHYz9VOtlqoSB--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20061111023051.38dbaa37>