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hitchhiker2006
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PostPosted: Sat Jan 24, 2009 3:29 am    Post subject: What is the arch for Intel Core Duo? Reply with quote

What's the appropriate cflags -march setting for Intel Core Duo?
I've seen both pentium-m and prescott used, which one is it?
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desultory
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PostPosted: Sat Jan 24, 2009 3:59 am    Post subject: Reply with quote

Prescott.
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rrbrussell
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PostPosted: Sun Jan 25, 2009 6:43 am    Post subject: Reply with quote

32-bit is prescott
64-bit is nocona
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desultory
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PostPosted: Sun Jan 25, 2009 7:56 am    Post subject: Reply with quote

Intel Core Duo is 32 bit, the Core 2 series introduced 64 bit instructions to the Core branded processors.
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Tech2008
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PostPosted: Sun Jan 25, 2009 6:03 pm    Post subject: pentium-m and prescott Reply with quote

march setting for Intel Core Duo?
I've seen both pentium-m and prescott used
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Naib
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PostPosted: Sun Jan 25, 2009 6:22 pm    Post subject: Reply with quote

Code:

 head /etc/make.conf
# These settings were set by the catalyst build script that automatically built this stage
# Please consult /etc/make.conf.example for a more detailed example
CFLAGS="-march=core2 -O2 -pipe -fomit-frame-pointer"# -ggdb"
CHOST="x86_64-pc-linux-gnu"
CXXFLAGS="${CFLAGS}"
CBUILD=${CHOST}

MAKEOPTS="-j4"
ACCEPT_KEYWORDS="~amd64"

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SlashBeast
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PostPosted: Sun Jan 25, 2009 6:45 pm    Post subject: Reply with quote

-fomit-frame-pointer is set by -O2 on x86_64.

core2 != core duo

Quote:
prescott
Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and
SSE3 instruction set support.

nocona
Improved version of Intel Pentium4 CPU with 64-bit extensions,
MMX, SSE, SSE2 and SSE3 instruction set support.

core2
Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3
and SSSE3 instruction set support
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n00b_admin
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PostPosted: Tue Jan 27, 2009 10:00 am    Post subject: Reply with quote

Intel Core 2 Duo T7200 here.

I use the "prescott" march since i'm running on 32 bit using gcc 4.1

Pay attention to the gcc version also.
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Geralt
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PostPosted: Tue Jan 27, 2009 11:15 am    Post subject: Reply with quote

Also note that with GCC 4.2 you can just write -march=native
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diejengent
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PostPosted: Wed Sep 26, 2012 11:13 am    Post subject: Reply with quote

I am very confused here....

My laptop contains: Intel Core Duo T2400 1.83 GHz, Family 6, Model 14

When I use the native option in gcc (latest version from portage september 2012) to determine my march, it returns "pentium-m".

The gentoo wiki suggests that my cpu is intel core duo and I should use "prescott" as march.

Which should I choose now? Or is the "pentium-m" option still better because of some kind of power management in the laptop?

Thanks in advance for your help :)
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fr3eatlast
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PostPosted: Wed Sep 26, 2012 7:30 pm    Post subject: Reply with quote

I would recommend looking at the Safe Cflags for Intel page which can be found here.

hth
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The Doctor
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PostPosted: Wed Sep 26, 2012 8:16 pm    Post subject: Reply with quote

Use -march=native now. It does this automatically.
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diejengent
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PostPosted: Wed Sep 26, 2012 10:05 pm    Post subject: Reply with quote

Thanks for your responses.

But what about what is discussed at this link:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45483

gentoo uses an older version of gcc and it this seems to contain a bug.


Last edited by diejengent on Thu Sep 27, 2012 12:07 am; edited 1 time in total
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diejengent
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PostPosted: Thu Sep 27, 2012 12:04 am    Post subject: Reply with quote

I have been doing some comparison with the following command:

echo "int main() { return 0; }" | gcc -march=prescott/pentium-m -v -Q -x c - 2>&1

The only difference is that prescott has the instruction -msse3 (SSE3) and pentium-m has not.
This is confirmed by the command cat /proc/cpuinfo which also seems to say my cpu has no SSE3.

How weird is it that the List of Intel microprocessors on Wikipedia says that my cpu DOES have SSE3?
I tried the program CPU-Z in Windows and this program indeed confirms my cpu has SSE3.

So how come in the Linux environment this is not recognized?
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diejengent
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PostPosted: Thu Sep 27, 2012 5:07 pm    Post subject: Reply with quote

I have been doing some research myself.
My CPU indeed supports SSE3, but in Linux it not seen as sse3, but with the other name that is also used for it: PNI (Prescott New Instructions).

I emerged gcc-4.6.3 and compared it's output with the stable version 4.5.4 while using the -march=native option.

output from gcc-4.5.4:

/usr/libexec/gcc/i686-pc-linux-gnu/4.5.4/cc1 -E -quiet -v - -D_FORTIFY_SOURCE=2 -march=pentium-m --param l1-cache-size=32 --param l1-cache-line-size=64 --param l2-cache-size=2048 -mtune=generic

output from gcc-4.6.3:

/usr/libexec/gcc/i686-pc-linux-gnu/4.6.3/cc1 -E -quiet -v - -march=pentium-m -mno-cx16 -mno-sahf -mno-movbe -mno-aes -mno-pclmul -mno-popcnt -mno-abm -mno-lwp -mno-fma -mno-fma4 -mno-xop -mno-bmi -mno-tbm -mno-avx -mno-sse4.2 -mno-sse4.1 --param l1-cache-size=32 --param l1-cache-line-size=64 --param l2-cache-size=2048 -mtune=generic

Seems there is indeed a bug residing in gcc-4.5.4 which was already discussed and fixed (see here: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45483).

Though, there is still one more bug remaining I think...
my CPU is an Intel Core Duo (in a laptop) and it has SSE3 (PNI in Linux), but march=native keeps saying my march is pentium-m. But with this march I am missing out on the SSE3 benefits.
What do you think? Am I right? Is this a 'bug'?
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