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Re: x86-64 on i386 (was Re: Promoting i386 version over x86_64?)



On Sun, 13 Dec 2009, drago01 wrote:

such a setup does not make much sense, when your hardware supports x86_64 not using it for userspace is a waste ....

a) i386 has a lower memory footprint, as has been mentioned in this
   thread.

b) The amount of code on your system that is CPU bound and/or
   memory-bound due to register pressure, to an extent that the x64
   registers would make an appreciable difference is probably not
   that significant

   - kernel hotpots
   - graphics hotspots (X server perhaps)

   I havn't measured this, but nor have the people who say x86_64 is
   faster AFAICT, and there's plenty of experience to say that most
   software is far from CPU bound or memory bound.

c) There is a definite cost to a distro in having to maintain 2
   x86_64 and i386 as separate arches

   - QA
   - package building and distribution

   Every supported arch increases the size of the test matrix.

   Minimising the number of arches you have to, say, test a "cp"
   bugfix against helps reduce QA load and helps you get better
   software to your users, faster (better cause you release time
   spent on architecture QA that can be spent on improving software
   generally).

d) Like or not, i386 is the de-facto standard for binary interfaces:

   - Netscape plugins
   - Windows executables

   The retort no doubt will "Oh but this is Fedora, we don't care
   about any closed-source stuff", but that would miss the point
   entirely re *Interface*. The i386 machine can be a plugin
   interface between 2 different open-source systems, e.g. consider:

   - VM images to run in, say, QEMU/KVM
   - Sandboxing technologies for, say, browser plugins (I think
     Google have stuff in this area)
   - Free software windows-only apps (don't know if they exist)

   All the code here can be open-source/free-software and still be
   relying on i386 as a widely known and hence convenient
   /interface/. As such, it likely needs to be supported on x86_64
   kernel-based systems anyway, as performantly as possible. (And
   yeah, I gather KVM x86_64 doesn't work for i386 VMs - annoying).

So personally I think x86_64-pure is unrealistic and, independently, I think 32-on-64 makes sense, but hey. :)

regards,
--
Paul Jakma	paul jakma org	Key ID: 64A2FF6A
Fortune:
He who despises himself nevertheless esteems himself as a self-despiser.
		-- Friedrich Nietzsche


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