12.04 LTS: 64-bit desktop by default?

[Pavel Rojtberg]

Am 16.04.2012 23:36, schrieb Scott Ritchie:
> On 4/16/12 9:25 AM, Steve Langasek wrote:
>> Hi Mike,
>>
>> On Mon, Apr 16, 2012 at 11:09:19AM -0400, Michael Terry wrote:
>>> On 16/04/12 02:03, Steve Langasek wrote:
>>>> 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.
>>
>>> There seems to be an unstated assumption that the default
>>> recommended architecture needs to stay the same throughout the
>>> lifecycle of 12.04 LTS.  Is that true?
>>
>> I don't see us making such a change for a point release.  First, we 
>> don't
>> typically get CDs pressed of point releases; second, there is going 
>> to be
>> some confusion on the part of users about this change, and I think we 
>> can
>> better mitigate that if changing it as part of .0 instead of as a point
>> release.
>>
>>> If we end up deciding to stick with i386 for now to better support
>>> common hardware, this question will still be re-evaluated for a
>>> future release.  And when it changes, we could go back and change
>>> the default download link and what is installed on the store USB
>>> sticks for 12.04 LTS.
>>
>> We could, but I'm pretty sure it's not worth it at that point.
>>
>
> Relatedly, I'm worried about what happens when these 12.04 users 
> upgrade to 14.04.  It would be really unfortunate to have them still 
> on 32 bit by that point.
>
> Unless, of course, we have ambitions of supporting automatic 
> cross-architecture upgrades by then.
>
> Thanks,
> Scott Ritchie
>
I would not bet that 14.04 users necessarily will have to get 64bit. 
There is the recent x32-abi[1] development which kind of combines best 
of both worlds.

This is also my concern with switching to 64bit by default. Most 
programs actually do not need more than 4GB virtual memory and thus 
64bit addresses are just a waste there.
Is there any evaluation taking into account the more aggressive compiler 
optimization used for 64bit. (like auto vectorisation, SSE2)
It would be interesting whether the performance gain really comes from 
the larger address space or those compile optimizations.

Greets,
Pavel

[1] http://en.wikipedia.org/wiki/X32_ABI