12.04 LTS: 64-bit desktop by default?

[Steve Langasek]

Hi folks,

Back at last UDS in November, we discussed whether it was time to switch to
presenting 64-bit images as the default image for desktop, like they already
are for server, now that all new desktop hardware is 64-bit and multiarch is
a reality.

There was a rough consensus at UDS that the blockers were solved, but that
the question should be taken to ubuntu-devel to gather more input.  That
input-gathering is happening much later than intended, but here we are now.

The blueprint at
<https://blueprints.launchpad.net/ubuntu/+spec/foundations-p-64bit-by-default>
includes links to some data gathered by the inimitable Colin King, showing
that in terms of performance, there are both pros and cons for switching to
amd64: memory consumption goes up, and therefore power consumption goes up
if the system is making more use of swap, but on the other side, most
CPU-bound operations will be faster on amd64.  So there is no clear
performance argument for preferring one over the other.

Where multiarch is concerned, we've made good progress on library coverage;
over 400 library packages are multiarch coinstallable in 12.04, including
most of the usual suspects in the desktop stack, and indeed there are two
packages in the partner repository now that are available only as i386
packages installable using multiarch, instead of using ia32-libs which is
now just a compatibility wrapper package.  So from what I've seen
compatibility with 32-bit binary software is in pretty good shape as well.

Are there problems that we've overlooked with regards to shipping 64-bit by
default on the desktop, or is it reasonable to make this switch for 12.04
LTS?  Is there 32-bit binary software that you know about which is not yet
supported on amd64 via multiarch, and ought to be before we consider making
64-bit the default?

Note that we're talking about three changes here:

 - Changing the default download link on ubuntu.com to point to 64-bit
   desktop images
 - Changing the pressed CDs distributed by Canonical to be 64-bit instead of
   32-bit
 - Changing the architecture used for preformatted USB disks sold in the
   Canonical shop

In general, if people can think of reasons not to switch to 64-bit for one
of these, those arguments would apply to the other; so if we think we're
ready for a switch, that switch should be applied across the board.

And regardless of which we decide to use as the default, both of amd64 and
i386 will continue to be supported architectures for the length of 12.04 LTS
and will remain available for download.

Feedback welcome!

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org
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