Actual benefits of amd64 over i386
obrien at freebsd.org
Tue May 24 10:53:24 PDT 2005
On Thu, May 19, 2005 at 02:01:36PM -0300, Joo Carlos Mendes Lus wrote:
> David O'Brien wrote:
> > On Fri, May 13, 2005 at 04:17:11PM -0300, Joo Carlos Mendes Lus wrote:
> >> What about a 64 bit kernel, and mixed mode (32bit and 64bit)
> >>userland? Solaris does this, and it sounds efficient, from the comments
> >>I've seen in this list.
> > When Sparc went from 32-bits to 64-bits the calling ABI was not changed.
> > Nor were the number of registers increased. So it is w/o a doubt that a
> > 32-bit Sparc binary runs faster than a 64-bit one (abit 64-bit math and
> > large memory). This is not true of AMD64 - the number of registers was
> > doubled and the calling ABI changed and optimized.
> Would these benefits outcome the losses caused by bigger binaries?
> Isn't it possible to use 64 bit registers in a 32 bit segment? Just
> like i386 segments, where one could define the default register size...
> > What is the difference of "i386 emulation" and "native 32 bit executables
> > in amd64 arch"??
> IMHO, the 32bit binaries prepared to run in amd64 32bit segments are
> not the same as 32 binaries prepared to run in i386 mode. These "32bit
> amd64 executables" would take advantage of the extra registers and 64
> bit extensions when possible.
It is not possible to access the extra registers in 32-bit mode.
-- David (obrien at FreeBSD.org)
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