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Date: Fri, 25 May 2007 19:03:37 +0200
From: "Andreas Claesson" <andreas.claesson@gmail.com>
To: gentoo-user@lists.gentoo.org
Subject: Re: [gentoo-user] which -march flag to pick for Intel Core 2 Duo in make.conf?
In-Reply-To: <AA0639A1EB70AE409130258CE7BDC31806646B17@messenger.cv63.navy.mil>
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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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