Re: [PATCH v6 2/9] x86/resctrl: Require 64-bit x86 for resctrl support

[Chen, Yu C]

On 8/24/2026 10:18 PM, Dave Hansen wrote:
> On 8/25/26 06:12, Chen Yu wrote:
> > "32-bit x86 is maintained for legacy reasons. New CPU features are generally
> > not enabled for 32-bit system, its test coverage keeps shrinking, and modern
> > 32-bit distributions have become rare."
>
> What would folks think about plopping something like the following text
> in to Documentation/arch/x86/32bit-kernels.rst ?
>
> Would that clear things up?

Thanks, Dave, for the detailed document. It will be very helpful.

> ---
>
> =========================================
> Supporting new features on 32-bit kernels
> =========================================
>
> While it is possible to compile and run a 32-bit kernel on 64-bit
> capable hardware, it is impractical and discouraged. Processors
> capable of running 64-bit kernels are expected to do so.
>
> The last 32-bit processor to come out of Intel or AMD was a Quark CPU
> in 2013. Before that the most recent were some Atom CPUs in 2008.
>
> Distros supporting 32-bit kernels and userspace are disappearing.  For
> example, in 2026 Ubuntu and Fedora no longer have support, with Debian
> being the most notable holdout still maintaining 32-bit options.

According to
https://www.debian.org/releases/trixie/release-notes/issues.en.html#i386-reduced-support
"From trixie, i386 is no longer supported as a regular architecture"

> New Processor Features
> ======================
>
> When adding support for a new processor feature in 2026 and beyond it
> should, by default, be:
>
>          config NEW_SNAZZY_CPU_FEATURE
>                  depends X86_64

depends on X86_64

thanks,
Chenyu

> This ensures that the folks developing this feature do not waste
> resources making it work on 32-bit kernels running on 64-bit hardware.
>
> It is also acceptable to add this restriction to existing processor
> features if 32-bit kernel support is adding maintenance burden,
> especially if the feature was only ever available on 64-bit processors.
>
> New Software Features
> =====================
>
> Let's say you are enhancing ftrace or adding a debugging feature that
> has no strict dependency on processor features. It does not need to
> be restricted to 64-bit only. But you might want to consider doing so
> if it simplifies your implementation.
>
> For instance, sometimes it adds complexity to support HIGHMEM. You may
> add a dependency on X86_64 in cases where it is impractical or simply
> challenging to support 32-bit kernels.