Date: Wed, 31 Jan 2007 19:06:36 -0800 From: Garrett Cooper <youshi10@u.washington.edu> To: freebsd-questions@freebsd.org Subject: Re: gcc compiler cputype, prescott or nocona confusion Message-ID: <45C1593C.8050003@u.washington.edu> In-Reply-To: <209e855bb68d64550ec4e384b3983664@mail.wcborstel.com> References: <200701312340.38593.salkillen@internode.on.net> <209e855bb68d64550ec4e384b3983664@mail.wcborstel.com>
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Jorn Argelo wrote: > > On Wed, 31 Jan 2007 23:40:38 +1100, Scott Killen <salkillen@internode.on.net> wrote: >> Hi, >> >> When recompiling the world or kernel in FreeBSD i386 Rel 6.1 with, >> >> "# make buildworld" >> or >> "# make buildkernel KERNCONF=MYSMPCONF" >> >> (or building anything anything else for that matter), even though I have >> "CPUTYPE?=nocona" set in my "/etc/make.conf" file the compiler seems to >> head >> back to a default of "-march=prescott" when compiling many of the >> functions >> on a Dual Xeon 3.6g (nocona) machine! >> >> This doesn't happen when compiling for other machine types, I've tried it >> on a >> Dual PentiumPro, Dual PII, Dual PIII setting the CPUTYPE to the correct >> cpu >> type and the -march sticks to the assigned cpu type through all operations >> and produces nice quick optimized code. >> >> Why is this so? >> >> Is it because the "nocona" machine type optimization refers to the EMT64 >> technology and thus is rejected when compiling for i386 targets rather >> than >> amd64 or emt64 targets and Gcc rejects it? > > That's right. AFAIK the Nocona core is a prescott with EM64T support (feel free to correct me if I am wrong). Basically you have an i386 version of FreeBSD, and with EM64T instructions enabled GCC will build a 64-bit version of FreeBSD. I think that's the reason it switches back to prescott. Most of the time you're right. However (for starters), some nocona chips feature 2MB cache instead of 1MB cache: <http://www.anandtech.com/IT/showdoc.aspx?i=2447&p=2>. I'd have to look more in depth, but OTOH the nocona also featured some architecture upgrades, other than just the "64-bit'ness" I heard that gcc 3.4.x was pretty funky with the nocona processors though, and prescott's a more stable target; that changed a bit in gcc 4.x I think. Or maybe I'm just mixing up nocona and yonah in this case. -Garrett
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