Re: __atomic_test_and_set() and mips o32 - help wanted

[David Brownlee <abs%netbsd.org@localhost>]

On Tue, 18 Nov 2025 at 12:59, Mouse <mouse%rodents-montreal.org@localhost> wrote:
>
> > Just trap and emulate LL/SC in the kernel for user software;
>
> I'm not sure the smartest option is to place the emulation load most on
> the machines with the least computational resources to spare.
>
> > newer hardware (which is the vast majority nowadays).
>
> NetBSD used to be about actually _supporting_ old hardware, not tyranny
> of the recent majority.

The conversation here is specifically about how to continue to support
that older hardware, in the face of gcc changes that would drop that
support without additional effort from NetBSD developers.

Older hardware is most likely to gain performance benefit from custom
kernels to make more space available, and that can extend to userland
builds. See NetBSD/mac68ksf where an entire new port has been added to
provide the best performance for a subset of older hardware.

I'm sure a compile time option to allow building a userland to better
target UP MIPS-1 machines would not be rejected.

MIPS-II debuted in 1990, and MIPS-III in 1991 with the R4000, and I
think even DEC had stopped shipping pre MIPS-III boxes by around 1994,
so we are talking about a diminishing number of very old boxes, and
*still* the discussion is around how to continue to support them.

Could I suggest that instead of complaining about those who are
continuing to try to support older hardware, a "Yes... and could we go
further and provide a way to build to optimise performance on the
oldest hardware" approach might yield a better response.

> If you want software that _supports_ old MIPS, I'd suggest old NetBSD.
> It might not help, but, depending on your use case, sit might be worth
> trying.
>
> If you have trouble finding it - I think ftp.netbsd.org no longer
> contains anything older than a version or two - I've got copies of
> versions from 1.0 to 6.1.2 I can hook you up with.  (I forget why I
> stopped at 6.1.2.)

https://ftp.netbsd.org/pub/NetBSD-archive/ looks to go all the way
back to NetBSD-1.0

Thanks

David