12.04 LTS: 64-bit desktop by default?

Kees Cook kees at ubuntu.com
Wed Apr 18 00:04:17 UTC 2012

On Tue, Apr 17, 2012 at 04:17:22PM -0700, Steve Langasek wrote:
> The key one is this: 25% of all (~16k) submissions to Ubuntu Friendly are
> from 32-bit machines.

Hrm. My sample[1] of x86 CPUs taken from Launchpad Bug reports in Nov 2009
is smaller (7264), but shows a change in adoption rate (4945 had "lm"
in /proc/cpuinfo), at 32% 32-bit. So 29 months later, 32-bitness has
fallen 7%. In 2021 we'll be 0% 32-bit! Well ahead of the 2038 bug! ;)

The problem, frankly, is this is all self-reporting, and doesn't have
anything to do with the target of "new installs".

> 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.

Upgrades will stay on whatever they had before. By definition then,
all data gathered about existing installs is out of date.

Regardless, going with the UF measurements, why are we penalizing 75% of
Ubuntu users? Their experience could be arguably better on 64-bit. It's
not like we're killing 32-bit. We've killed entire architectures when new
installs hit 5%. It doesn't seem like it makes sense to wait to change
the _default_. If things get much lower, people will just want to remove
the arch entirely. For an LTS, it seems all the more critical to produce
defaults that will make sense for 5 years. (Assuming the linear 0.24%
drop per month, at the end of 12.04's LTSness, 14% of the user base will
have 32-bit CPUs -- seems like it'd be way overdue to change the default
by then.)

> 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.

Yeah, fixing this would go a long way toward solving the educational

> 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.

How about changing the way the web presents the default, and move it
to 64-bit? For example...

   Download Ubuntu 12.04 [64-bit] (not sure? Try [32-bit] instead)

> 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.

It seems like I should start trying to deprecate 32-bit so changing the
default to 64-bit seems like a less radical idea. :)


[1] http://bazaar.launchpad.net/~cpu-checker-dev/cpu-checker/trunk/files/head:/test/

Kees Cook

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