12.04 LTS: 64-bit desktop by default?

Steve Langasek steve.langasek at ubuntu.com
Tue Apr 17 23:17:22 UTC 2012

Thanks to all for the feedback so far.

Although discussion on the mailing list has been generally in favor of this
change, I've come into the possession of additional facts over the past
couple of days which I think tip the balance.

The key one is this: 25% of all (~16k) submissions to Ubuntu Friendly are
from 32-bit machines.

Now, this doesn't look at how the ratio is changing over time; but Ubuntu
Friendly is itself still a fairly recent initiative, so I don't expect this
to have changed much.  Switching our default image to a version that just
plain won't work on nearly a quarter of the machines users want to use it on
strikes me as a non-starter.  That's a much higher percentage than anyone
was expecting based on the UDS discussion.

That also ignores the machines that have 64-bit capable CPUs, but have only
1GB of RAM and therefore are better off sticking with 32-bit due to memory

Additionally, as mentioned in this thread, the message presented to users
when they try to boot a 64-bit image on a 32-bit machine is jargon-y
("kernel"; "x86_64").  A bug has been filed about this and should be fixed
soon, but I don't think it makes sense for us to commit to 64-bit by default
in the current state.

So while amd64 is clearly the better option for 64-bit machines with more
than 2GB of RAM, it looks like it would be premature to make this the
default.  Faced with a choice between a default that will be less efficient
on higher-end machines, and a default that will fail to boot at all on a
quarter of machines, I think we need to be conservative here and stay with
32-bit by default in 12.04.  I will therefore not be asking the web team to
point at the amd64 desktop image as the default.

I'll work with the Ubuntu Friendly team to monitor changes in the adoption
of 64-bit CPUs for future releases; and of course users who know amd64 is a
good fit for them are encouraged to use it in 12.04 LTS as well, since both
amd64 and i386 remain fully-supported options in this release.

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

On Sun, Apr 15, 2012 at 11:03:14PM -0700, Steve Langasek wrote:
> 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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