Linux Kernel Developers Discuss Dropping A Bunch Of Old CPUs

[phoronix]

Phoronix: Linux Kernel Developers Discuss Dropping A Bunch Of Old CPUs

With Linux 5.10 having shipped as the latest Long Term Support (LTS) release to be maintained for at least the next five years, a discussion has begun over dropping a number of old and obsolete CPU platform support currently found within the mainline kernel. For many of the architectures being considered for removal they haven't seen any new commits in years but as is the case once proposals are made for them to be removed there are often passionate users wanting the support to be kept...

http://www.phoronix.com/scan.php?page=news_item&px=2021-Linux-Drop-Old-CPUs

[uid313]

Is there any benefit to removing these other than less lines of code in the kernel, and less to maintain?
Example maybe removing 486 will that somehow maybe be possible to improve the kernel in some way to make it cleaner, faster, more stable or more secure?

[EvilHowl]

Is there any benefit to removing these other than less lines of code in the kernel, and less to maintain?
Example maybe removing 486 will that somehow maybe be possible to improve the kernel in some way to make it cleaner, faster, more stable or more secure?

Isn't 486 a very bad example? It's x86, so it should share a lot of code with modern x86 CPUs.

[Guest]

I remember seeing some bounty for adding m68k support in LLVM. I wonder how they feel about it's potential removal from the kernel.

[oiaohm]

https://github.com/MiSTer-devel/ao486_MiSTer

The 486DX dropping may not really be good idea. Thinking ao486 here gives a 486 on new FPGA chips. I can understand dropping some of those on the list due to the fact they are no longer made and don't have a FPGA emulation. Think about it to run test suites to make sure builds are good you really do need to have hardware in some what of a decent state.

Something I don't think exists for Linux is a automated testing setup using FPGA for testing legacy hardware.

[Chewi]

I remember seeing some bounty for adding m68k support in LLVM. I wonder how they feel about it's potential removal from the kernel.

It doesn't look like they want to remove it entirely, just for the more obscure hardware. I make use of the Amiga and Atari support and those are not in the list.

[jabl]

It doesn't look like they want to remove it entirely, just for the more obscure hardware. I make use of the Amiga and Atari support and those are not in the list.

Yes, like the mail says "atari/amiga/mac and coldfire are very much alive", those m68k targets are not going to be dropped.

[jabl]

Is there any benefit to removing these other than less lines of code in the kernel, and less to maintain?
Example maybe removing 486 will that somehow maybe be possible to improve the kernel in some way to make it cleaner, faster, more stable or more secure?

Removing support for old x86 cpu's can make the code slightly cleaner as you can unconditionally assume that newer features are present. 386 support, which was removed in 2012, thus bumping the minimum to 486, was kind of nice as there was some ugly 386-specific page table handling code and atomics code that they could get rid of. Getting rid of 486 doesn't seem to have such a big benefit, per https://en.wikipedia.org/wiki/X86_instruction_listings there's CPUID, RDTSC, CMPXCHG8B, {RD,WR}MSR.

[milkylainen]

I don't mind any of the gone for latest 5.10+ LTS.
I'm a bit surprised about the C6x though.
Maybe that support was always shitty so it has to go anyway?

[kpedersen]

Looking at these stats, it seems to suggest that the vast majority is amd64 and i686.

https://linux-hardware.org/index.php?view=os_arch

Almost everything else including aarch64 (1.1%), armv7l (0.3%), and others (0.1%) can be dropped

Even i686 is only 3% but if that is going to go, then ARM is going to have to go first.

(Yes these stats are likely unreliable and have very low numbers of results but... to be fair, probably still show valid trends).