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List:       ubuntu-devel-discuss
Subject:    Re: Proposal: Let's drop i386
From:       Henri Sivonen <hsivonen () hsivonen ! fi>
Date:       2018-07-01 16:08:02
Message-ID: CAJQvAudvZ+ndO5KHTYX1tj5ZoC1pbZSChngBxYGZ=tEj9OfV=w () mail ! gmail ! com
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On Sun, May 13, 2018 at 9:48 PM, Henri Sivonen <hsivonen@hsivonen.fi> wrote:
> On Sun, May 13, 2018 at 9:34 PM, Matthias Klose <doko@ubuntu.com> wrote:
>> On 13.05.2018 05:00, Henri Sivonen wrote:
>>> On Thu, May 10, 2018 at 11:25 PM, Thomas Ward <teward@thomas-ward.net> wrote:
>>>> However, killing i386 support globally could introduce issues, including
>>>> but not limited to certain upstream softwares having to go away
>>>> entirely, due to the interdependency or issues with how certain apps
>>>> work (read; Wine, 32-bit support, 64-bit support being flaky, and
>>>> Windows apps being general pains in that they work on 32bit but not
>>>> always on 64-bit).
>>>
>>> If 32-bit x86 support becomes mainly a thing that's run on x86_64
>>> hardware as a compatibility measure for things like Wine, it would
>>> make sense to bring the instruction set baseline to the x86_64 level.
>>> Specifically, it would make sense to compile the 32-bit x86 packages
>>> with SSE2 unconditionally enabled.
>>>
>>> This would mean dropping support for Pentium Pro and earlier or Athlon
>>> XP and earlier, but it's pretty sad to leave all that performance on
>>> the table in order to support the few computers still in use that have
>>> Pentium Pro or earlier or Athlon XP or earlier.
>>>
>>> As upstream software assumes SSE2 as the baseline, it will be less and
>>> less a run-time check and compiling software without SSE2 will mean
>>> shipping it in a damaged form performance-wise.
>>
>> I disagree, until you provide data how many packages fail to build, at least in
>> the testsuites, when run without the extra x87 precision bits.
>
> I don't have this data, but considering that SSE2 is a mandatory part
> of x86_64, it seems implausible that packages would be
> SSE2-intolerant. Considering that x86_64 defaults to SSE2
> floating-point math (or does Ubuntu override this?) and considering
> that ARM doesn't have x87 available, it seems implausible that
> packages would rely on x87. (On the contrary, since e.g. Firefox and
> Chromium upstreams don't do non-SSE2 x86 builds anymore, it seems more
> plausible that there exist packages whose upstream doesn't test x87
> floating-point math anymore.)

As a datapoint, Fedora is pursuing compiling 32-bit x86 packages with
SSE2 unconditionally enabled (including SSE floating-point math):
https://fedoraproject.org/wiki/Changes/Update_i686_architectural_baseline_to_include_SSE2

-- 
Henri Sivonen
hsivonen@hsivonen.fi
https://hsivonen.fi/

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