gcc compiler cputype, prescott or nocona confusion
youshi10 at u.washington.edu
youshi10 at u.washington.edu
Thu Feb 1 21:42:11 UTC 2007
On Thu, 1 Feb 2007, Jorn Argelo wrote:
> Garrett Cooper wrote:
>> Jorn Argelo wrote:
>>>
>>> On Wed, 31 Jan 2007 23:40:38 +1100, Scott Killen
>>> <salkillen at 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
>
> Yonah is the Pentium M version of the first Core generation I believe. Or maybe
> it was still a Netburst, I can't remember.
>
> Jorn
Yonah is the first version of the Core Duo generation processors.
-Garrett
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