Linus Torvalds Says it is Time to Get Rid of i486 CPU Support

After dropping support for the ancient i386 line of CPUs, over a decade back, the Linux Kernel is gearing up to possibly drop the i486 line of CPUs.

The i486 series of CPUs was launched back in 1989, and very few Linux distros, such as Gentoo, Slackware, and KNOPPIX support it nowadays.

Linus Torvalds mentioned dropping the support in the kernel mailing list:

We got rid of i386 support back in 2012. Maybe it's time to get rid of i486 support in 2022?

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Good or Bad News? 🤨

Well, I am afraid that it is bad news but it does not have a major impact.

You see, the i486 line of CPUs was developed by Intel in 1989 and had been losing relevance since its discontinuation back in 2007.

In the mailing list thread, Linus also adds more details involving this change while changing the base requirement of the Linux Kernel:

Maybe we should just bite the bullet, and say that we only support x86-32 with 'cmpxchg8b' (ie Pentium and later).

Get rid of all the "emulate 64-bit atomics with cli/sti, knowing that nobody has SMP on those CPU's anyway", and implement a generic x86-32 xchg() setup using that try_cmpxchg64 loop.

I think most (all?) distros already enable X86_PAE anyway, which makes that X86_CMPXCHG64 be part of the base requirement.

Not that I'm convinced most distros even do 32-bit development anyway these days.

One of the main reasons for this is the amount of work required to create workarounds for such an old CPU architecture to work on newer Linux Kernels.

Doing so also results in broken support that creates weird bugs and glitches.

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Of course, the i486 line of CPUs is ancient history. It's not just Linus Torvalds, I think we can all agree on that front. He also mentions that it is not relevant anymore from a kernel development standpoint, and very few are developing new hardware based on that architecture.

He intends to move the baseline to the cmpxchg8b instruction set, supported by processors such as the Pentium series and later. Doing so will see the minimum processor requirements for Linux Kernel step up to Pentium.

If you ask me, this is a good thing, I think it is time to retire support for i486 CPUs from the Linux Kernel. 🤔

It seems to be holding back the kernel to some extent and is causing unnecessary bugs that may require a lot of time and patience.

A few people might get upset over this, but it is a gamble that Linus and the others have to take to progress with the development of the Linux Kernel.

💬 What do you think? Should i486 support be dropped in favor of fewer bugs?

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