Date: Mon, 27 Mar 2006 16:41:00 -0500 From: Kris Kennaway <kris@obsecurity.org> To: Nikolas Britton <nikolas.britton@gmail.com> Cc: freebsd-stable@freebsd.org, Kris Kennaway <kris@obsecurity.org> Subject: Re: -march=pentium2 + -mtune=pentium4 faster then -march=pentium4? Message-ID: <20060327214100.GB73596@xor.obsecurity.org> In-Reply-To: <ef10de9a0603271333i591b2fa5x3ed8e8cb2c27198c@mail.gmail.com> References: <ef10de9a0603271105v3f68bd69q883e853366fb36d@mail.gmail.com> <20060327192044.GA70891@xor.obsecurity.org> <ef10de9a0603271333i591b2fa5x3ed8e8cb2c27198c@mail.gmail.com>
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--lEGEL1/lMxI0MVQ2 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Mar 27, 2006 at 03:33:09PM -0600, Nikolas Britton wrote: > On 3/27/06, Kris Kennaway <kris@obsecurity.org> wrote: > > On Mon, Mar 27, 2006 at 01:05:13PM -0600, Nikolas Britton wrote: > > > Why does GCC produce faster code using "-march=3Dpentium2 > > > -mtune=3Dpentium4" on a Pentium 4 chip versus plain -march=3Dpentium4? > > > > > > Try it... > > > > > > CPUTYPE=3Dpentium2 > > > CFLAGS+=3D -mtune=3Dpentium4 > > > COPTFLAGS+=3D -mtune=3Dpentium4 > > > > Talk to the gcc developers (and provide benchmarks). > > >=20 > What would be an adequate, proof, benchmark? Heh..one presumes you already have such a thing (e.g. nbench as you say below), and that you've carefully measured it in order to formulate your conclusion. "Carefully measured" means the usual benchmarking rules like running your test many times and computing statistics (e.g. using ministat), and making sure your only variable is the thing you think it is, etc. > I've already run several > tests with nbench, testing all of the possible configurations of > -march and -mtune. Kris --lEGEL1/lMxI0MVQ2 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2.2 (FreeBSD) iD8DBQFEKFvrWry0BWjoQKURArriAKChXl5opRak9MpssV6I0LBzldQQ3gCg+PpT WEDFKuVxRUPT9PBWw7NvGiQ= =24sU -----END PGP SIGNATURE----- --lEGEL1/lMxI0MVQ2--
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