Re: [gentoo-dev] Gentoo i486 support

[Andrew Savchenko]

Hi!

On Wed, 22 Aug 2018 09:08:06 -0400 Rich Freeman wrote:
> On Wed, Aug 22, 2018 at 8:26 AM Ben Kohler <bkohler@g.o> wrote:
> >
> > 1) Adjust x86 profile defaults to drop the problematic -march=i686.
> > This would be more in line with amd64 profiles (et al), which set no
> > -march value so it can run on any hardware for this arch.
> >
>
> My knee-jerk reaction was that this is a bad idea, but after a bit of
> thought there are some arguments in favor of this:
>
> First, the argument against: i386 is VERY old.  Most distros moved
> their defaults to i686 because it had significant improvements, and
> i686 was still mainstream but i386 was ancient.  In contrast with
> amd64 the entire architecture is fairly new and the baseline doesn't
> suffer from many of the issues i386 suffers compared to i686.  This is
> a really short synopsis - if you go to any distro list archive you can
> find long passionate arguments from ~10 years ago that elaborated on
> this.  In that sense, going back to i386 is turning back the clock.
>
> HOWEVER, I think there is an argument for i386 that wasn't so valid
> back then.  x86 in general is starting to look a bit like i386.  What
> are the main use cases for it in this day and age?  I don't use x86,
> so I'm not the best person to answer that.  However, I'd broadly split
> it into two categories (mostly by tautology):
>
> 1.  Museum hardware.  People have systems that are running simply
> BECAUSE they are old, not because they are cost-effective/etc.  I'm
> not sure I'd even lump used hardware into this category any longer, as
> I'm sure there are plenty of i686+ used PCs at rock-bottom prices
> already out there, and maintaining pre-Y2K hardware is going to be
> fairly painful.  For this use case i386 as the baseline makes a LOT of
> sense.
>
> 2.  Non-museum hardware.  People have x86 hardware because it is the
> most cost-effective solution for a task, and not merely because it is
> old.  IMO for this use case i686 makes a lot more sense as a baseline.
> However, I'm honestly not sure in this day and age what these use
> cases even are, unless it is something you can buy for $10 at a flea
> market.  Even if you're talking about a container running one
> application that only needs 500kB of RAM, is there really that much
> benefit to not building it for amd64?

As active x86 hardware user I can add:

3. Security. CPUs without speculative execution and L3 cache are
much more secure by design. Thanks to the virtues of Gentoo
(highest possible code optimization and ability to USE light
versions of applications) such hardware (e.g. 32bit Atoms) is still
usable quite fine.

Best regards,
Andrew Savchenko