Date: Tue, 24 May 2005 10:53:15 -0700 From: "David O'Brien" <obrien@freebsd.org> To: =?unknown-8bit?Q?Jo=E3o_Carlos_Mendes_Lu=EDs?= <jonny@jonny.eng.br> Cc: freebsd-amd64@freebsd.org Subject: Re: Actual benefits of amd64 over i386 Message-ID: <20050524175315.GA35171@dragon.NUXI.org> In-Reply-To: <428CC670.50002@jonny.eng.br> References: <BEA97082.3CD55%michael.hopkins@hopkins-research.com> <42842F46.9040608@samsco.org> <4284FD37.2070009@jonny.eng.br> <20050519054630.GC68698@dragon.NUXI.org> <428CC670.50002@jonny.eng.br>
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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@FreeBSD.org)
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