Re: Can we drop upstream Linux x32 support?

From: Olof Johansson
Date: Thu Dec 13 2018 - 09:39:07 EST

On Tue, Dec 11, 2018 at 9:40 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Dec 10, 2018 at 5:23 PM Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> >
> > I'm seriously considering sending a patch to remove x32 support from
> > upstream Linux. Here are some problems with it:
> I talked to Arnd (I think - we were talking about all the crazy ABI's,
> but maybe it was with somebody else) about exactly this in Edinburgh.
> Apparently the main real use case is for extreme benchmarking. It's
> the only use-case where the complexity of maintaining a whole
> development environment and distro is worth it, it seems. Apparently a
> number of Spec submissions have been done with the x32 model.
> I'm not opposed to trying to sunset the support, but let's see who complains..

I'm just a single user. I do rely on it though, FWIW.

I hadn't finished my benchmarking in Edinburgh, but for my new machine
that does kernel builds 24/7, I ended up going with x32 userspace (in
a container).

Main reason is that it's a free ~10% improvement in runtime over
64-bit. I.e. GCC-as-a-workload is quite a bit faster as x32,
supposedly mostly due to smaller D cache footprints (I ran out of
cycles to tinker with back and forth perf data collection and settled
down on just running it).

Running classic 32-bit (i386? i686? whatever it's called) is about
half as good. I.e. even then I get a ~5% performance win. Less than
x32, but still better than 64-bit userspace.