[gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Denis]

Are these any options in the kernel and in the gcc to optimize for
Intel's Core 2 Duo chips?  When I set up my gentoo box for the Pentium
Processor Extreme Edition (dual core prescott), I just used
-march=prescott in make.conf

Which -march flag would be the most relevant gcc optimization for
Intel Core 2 Duo?

And is there explicit support in the latest gentoo kernel for Core 2
Duo, or does it go under Pentium 4 family?

Thanks
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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Ryan Sims]

On 5/24/07, Denis <denis.che@gmail.com> wrote:
> Are these any options in the kernel and in the gcc to optimize for
> Intel's Core 2 Duo chips?  When I set up my gentoo box for the Pentium
> Processor Extreme Edition (dual core prescott), I just used
> -march=prescott in make.conf
>
> Which -march flag would be the most relevant gcc optimization for
> Intel Core 2 Duo?
>
> And is there explicit support in the latest gentoo kernel for Core 2
> Duo, or does it go under Pentium 4 family?
>

Google is your friend:
http://www.google.com/search?q=core+2+duo+cflags
http://gentoo-wiki.com/Safe_Cflags#Intel_Core_2_Duo.2FQuad_.2F_Xeon_51xx.2F53xx



-- 
Ryan W Sims
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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Mark Shields]

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On 5/24/07, Denis <denis.che@gmail.com> wrote:
>
> Are these any options in the kernel and in the gcc to optimize for
> Intel's Core 2 Duo chips?  When I set up my gentoo box for the Pentium
> Processor Extreme Edition (dual core prescott), I just used
> -march=prescott in make.conf
>
> Which -march flag would be the most relevant gcc optimization for
> Intel Core 2 Duo?
>
> And is there explicit support in the latest gentoo kernel for Core 2
> Duo, or does it go under Pentium 4 family?
>
> Thanks
> --
> gentoo-user@gentoo.org mailing list
>
>
A gentoo forum thread[1] states to use -march=nocona for Core 2 Duo, and
-march=prescott for Core  Solo/Duo.

[1] http://forums.gentoo.org/viewtopic-p-3602555.html


-- 
- Mark Shields

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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Denis]

After reading some docs, the impression I get is that the 'nocona'
flag is for building a 64-bit system...  For a 32-bit system, it seems
like 'prescott' would be the choice, wouldn't it?

This from the GCC website about 4.2.0 release changes:

IA-32/x86-64

    * -mtune=generic can now be used to generate code running well on
common x86 chips. This includes AMD Athlon, AMD Opteron, Intel
Pentium-M, Intel Pentium 4 and Intel Core 2.
    * -mtune=native and -march=native will produce code optimized for
the host architecture as detected using the cpuid instruction.
    * Added a new command line option -fstackrealign and and
__attribute__ ((force_align_arg_pointer)) to realign the stack at
runtime. This allows functions compiled with a vector-aligned stack to
be invoked from legacy objects that keep only word-alignment.

We don't have gcc-4.2.0 in our portage available for installation yet,
do we?  Anyone know when?
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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Neil Bothwick]

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On Thu, 24 May 2007 11:13:30 -0400, Denis wrote:

> After reading some docs, the impression I get is that the 'nocona'
> flag is for building a 64-bit system...  For a 32-bit system, it seems
> like 'prescott' would be the choice, wouldn't it?

Yes.


> We don't have gcc-4.2.0 in our portage available for installation yet,
> do we?  Anyone know when?

When the devs consider it suitable for at least the testing branch or
when you do "echo =sys-devel/gcc-4.2*" >>/etc/portage/package.mask,
whichever comes sooner.

Bear in mind that GCC is almost certainly masked for good reason. It's
not like you're using a binary distro and only need a compiler for a few
packages. Feel free to try it in the knowledge that if it breaks your
system, you get to keep the pieces.


-- 
Neil Bothwick

Sects, sects, sects, is that all you monks think about?

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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Graham Murray]

Neil Bothwick <neil@digimed.co.uk> writes:

> When the devs consider it suitable for at least the testing branch or
> when you do "echo =sys-devel/gcc-4.2*" >>/etc/portage/package.mask,
> whichever comes sooner.

Even that will not work (yet) as gcc-4.2 is not actually masked it is
not keyworded.
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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Denis]

On 5/24/07, Neil Bothwick <neil@digimed.co.uk> wrote:
> Bear in mind that GCC is almost certainly masked for good reason. It's
> not like you're using a binary distro and only need a compiler for a few
> packages. Feel free to try it in the knowledge that if it breaks your
> system, you get to keep the pieces.

Ain't it the truth!  No, I wasn't asking with the anxiety to hurry
things up - I was asking more about an estimated release time, whether
it will be a month, 2 months, 3 months, etc.

I'm not really looking to "experiment" with the cutting-edge releases
right now.  My aim is to build a fast, stable system for my
computations, which ultimately brought me to another major decision:
32-bit or 64-bit...  I run simulations which I write in C and
numerical computations which I run in Mathematica (which has just
released the 64-bit version).  Would a 64-bit system significantly
benefit these applications?
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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Randy Barlow]

On Thu, May 24, 2007 12:38 pm, Denis wrote:
> My aim is to build a fast, stable system for my
> computations, which ultimately brought me to another major decision:
> 32-bit or 64-bit...  I run simulations which I write in C and
> numerical computations which I run in Mathematica (which has just
> released the 64-bit version).  Would a 64-bit system significantly
> benefit these applications?

If you are using a lot of memory in your computations, then the 64-bit
environment will be much friendlier to you :)  Also, if I understand
correctly, you will get higher precision on floating point calculations
(someone correct me if I am wrong here!)  I also believe that the 64 bit
processors are able to perform more instructions per second on average
when executing 64 bit code vs. 32 bit code if I am not mistaken...

-- 
Randy Barlow
http://www.electronsweatshop.com
"Oh me of little faith..."
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[gentoo-user] Re: which -march flag to pick for Intel Core 2 Duo in make.conf?

[Alexander Skwar]

Denis <denis.che@gmail.com> wrote:

> Are these any options in the kernel and in the gcc to optimize for
> Intel's Core 2 Duo chips?

In the kernel: Yes. At least in 2.6.21. 

> And is there explicit support in the latest gentoo kernel for Core 2
> Duo, or does it go under Pentium 4 family?

I'd say, it goes under Core2 -> MCORE2.

Alexander Skwar

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RE: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[burlingk]

> -----Original Message-----
> From: Randy Barlow [mailto:randy@electronsweatshop.com] 
> Sent: Friday, May 25, 2007 4:23 PM
> To: gentoo-user@lists.gentoo.org
> Subject: Re: [gentoo-user] which -march flag to pick for 
> Intel Core 2 Duo in make.conf?
> 
<Snip>

> If you are using a lot of memory in your computations, then 
> the 64-bit environment will be much friendlier to you :)  
> Also, if I understand correctly, you will get higher 
> precision on floating point calculations (someone correct me 
> if I am wrong here!)  I also believe that the 64 bit 
> processors are able to perform more instructions per second 
> on average when executing 64 bit code vs. 32 bit code if I am 
> not mistaken...

I am not sure, but that makes sense.  If nothing else, things executed
directly usually run more smoothly than those who are run through
emulation.  64bit code on 64bit processor good...
^_^
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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Andreas Claesson]

On 5/25/07, burlingk@cv63.navy.mil <burlingk@cv63.navy.mil> wrote:
>
> > -----Original Message-----
> > From: Randy Barlow [mailto:randy@electronsweatshop.com]
>
> <Snip>
>
> > If you are using a lot of memory in your computations, then
> > the 64-bit environment will be much friendlier to you :)
> > Also, if I understand correctly, you will get higher
> > precision on floating point calculations (someone correct me
> > if I am wrong here!)  I also believe that the 64 bit
> > processors are able to perform more instructions per second
> > on average when executing 64 bit code vs. 32 bit code if I am
> > not mistaken...
>
> I am not sure, but that makes sense.  If nothing else, things executed
> directly usually run more smoothly than those who are run through
> emulation.  64bit code on 64bit processor good...

There is no emulation involved when running 32bit code in either core2
 nor amd64 processors. The difference when running in 32bit mode is
that some instructions are unavailable, you have a smaller number of
registers, and the registers are only 32bit.

More registers speed up most kind of code, 64bit registers speed up
64bit calculations, and the extra instructions are good for array
calculations and similar (more sse instructions for example).

The only bad thing with 64bit code is that the programs get bigger,
which may effect memory performance negatively. But if you have a lot
of memory then you will benefit from not needing any special
addressing modes.

Since you (Denis) are doing a lot of mathematical calculations you
will probably benefit from running in 64bit mode.
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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Denis]

On 5/25/07, Andreas Claesson <andreas.claesson@gmail.com> wrote:
> Since you (Denis) are doing a lot of mathematical calculations you
> will probably benefit from running in 64bit mode.

I often need to run Monte Carlo simulations (in C) which involve a lot
of array storage and array scanning/searching operations...  I wonder
what the speed-up would be for those simulations if run under a 64-bit
mode.  Are there any requirements on how the simulations should be
programmed in order to take advantage of the 64-bit arch, or is that
automatically done by the GCC compiler and the kernel?
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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Randy Barlow]

Denis wrote:
> I often need to run Monte Carlo simulations (in C) which involve a lot
> of array storage and array scanning/searching operations...  I wonder
> what the speed-up would be for those simulations if run under a 64-bit
> mode.  Are there any requirements on how the simulations should be
> programmed in order to take advantage of the 64-bit arch, or is that
> automatically done by the GCC compiler and the kernel?

Just use the -m64 flag when you compile using gcc.

R
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Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?

[Dan Farrell]

On Fri, 25 May 2007 14:26:32 -0400
Denis <denis.che@gmail.com> wrote:

> On 5/25/07, Andreas Claesson <andreas.claesson@gmail.com> wrote:
> > Since you (Denis) are doing a lot of mathematical calculations you
> > will probably benefit from running in 64bit mode.
> 
> I often need to run Monte Carlo simulations (in C) which involve a lot
> of array storage and array scanning/searching operations...  I wonder
> what the speed-up would be for those simulations if run under a 64-bit
> mode.  Are there any requirements on how the simulations should be
> programmed in order to take advantage of the 64-bit arch, or is that
> automatically done by the GCC compiler and the kernel?

Would you mind telling us what kind of performance difference you
experience?
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