linux-kernel - Re: [PATCH v3 2/6] futex2: Implement vectorized wait

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Message-ID: <CAK8P3a3Bka5R4dmHE_+xuKTCtMaSZEYvT9jAz7QbgnF_CkeoNQ@mail.gmail.com>
Date:   Thu, 16 Sep 2021 13:50:14 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Gabriel Krisman Bertazi <krisman@...labora.com>,
        André Almeida <andrealmeid@...labora.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Darren Hart <dvhart@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Collabora kernel ML <kernel@...labora.com>,
        Linux API <linux-api@...r.kernel.org>,
        GNU C Library <libc-alpha@...rceware.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v3 2/6] futex2: Implement vectorized wait

On Thu, Sep 16, 2021 at 1:22 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Sep 16, 2021 at 12:10:25AM -0400, Gabriel Krisman Bertazi wrote:
>
> > I find this weird.  I'm not even juts talking about compat, but even on
> > native 32-bit. But also, 32 applications on 64, which is a big use
> > case for games.
>
> Seriously, people still make 32bit applications today? And for legacy
> games, I would think the speed increase of modern CPUs would far offset
> this little inefficiency.

There are 32-bit Windows games apparently, because it's easier to build it
that way than having both 32-bit and 64-bit versions.
There may be native 32-bit games built for Linux from the same sources when
that is not written portably, not sure if that's a thing.

One important reason to use compat mode is for cost savings when you can
ship an embedded system with slightly less RAM by running 32-bit user space
on it. We even still see people running 32-bit kernels on Arm boxes that have
entry-level 64-bit chips, though I hope that those will migrate the
kernel to arm64
even when they ship 32-bit user space.

Similar logic applies to cloud instances or containers. Running a 32-bit
Alpine Linux in a container means you can often go to a lower memory
instance on the host compared to a full 64-bit distro.

        Arnd