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386-DX/SX support nuked from Linux Kernel

git.kernel.org

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Re: 386-DX/SX support nuked from Linux Kernel

#23

Post by yuhong »

smegel wrote: post #22

I never really got why back support should be an issue - its all x86 instructions, if only a subset of what is used today right? I'm curious to know exactly what makes supporting old cpus so hard.

The x86 features in question are relatively small but pretty important nowadays. CMPXCHG and XADD are important atomic operations, for example.

Re: 386-DX/SX support nuked from Linux Kernel

#24

Post by JeremyMorgan »

kev009 wrote: post #13
frogurt wrote: post #5

I would have thought that support for this architecture would have been useful to keep, since a lot of rad-hardened systems (think space, satellite applications) still use it.

I'm into retrocomputing so these kinds of retirements always sting a bit. In realistic long term operations, deprecations don't hurt. I.e. your air traffic control system running on PA-RISC and HP-UX doesn't care that HP-UX only run on Itanium now. You keep running the old software and set up some kind of support schedule to keep the system patched during it's service life through the vendor or otherwise.

It's comforting to know others are interested in "retrocomputing". For some reason I like slow old computers too. (Not being sarcastic here at all)

Re: 386-DX/SX support nuked from Linux Kernel

#25

Post by JeremyMorgan »

I love old hardware big time, but if the current kernel can be trimmed up, let's do it. Those older machines probably shouldn't be rocking the latest kernel anyway.

I'm typing this from a 2004 PPC Powerbook running Ubuntu 10.04. There are a lot of packages and software I simply can't get anymore. But it's ok, because it doesn't have the power to run them anyway. It's frozen in time, and I know that. Anyone running on relying on 386 stuff should just stick with the older software that's working and pray they don't have a hardware failure. If the kernel starts packratting stuff it's going to be bloated and huge and it will hinder future development.

Maybe they should set a time limit on stuff, like 10 years before they drop support, or maybe 15 for the military and law offices.

Re: 386-DX/SX support nuked from Linux Kernel

#28

Post by [deleted] »

j45 wrote: post #12

386's were the first computers I ever used Linux on. Man. I will say this much, a 386 sx/16 was a large part of learning learn how to get so much done with so little resources. It's amazing how Linux was more efficient than windows even then, while the decade of driver drought was being bridged.

[deleted]

Re: 386-DX/SX support nuked from Linux Kernel

#29

Post by bdonlan »

smegel wrote: post #22

I never really got why back support should be an issue - its all x86 instructions, if only a subset of what is used today right? I'm curious to know exactly what makes supporting old cpus so hard.

It's not just instructions - it's CPU bug workarounds, too. For example, some 386s did not honor the write-protect bit in the page table when in supervisor mode. Now, since Linux normally does copies from kernel to userspace by writing straight to userspace and letting the WP bit detect writes to read-only memory, it's a problem if the WP bit doesn't work (it'd let you overwrite write-protected userspace memory). So Linux had a check that tested (at boot time) whether WP worked properly in supervisor mode, and if so it would set a flag to perform a slower, software-checked copy. This adds overhead to _every_ copy from kernel to userspace, as it needs to check this flag, and branch to the fallback implementation.
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