Re: Espresso (Nintendo Wii U) SMP build support

[Kurt Stine]

>If we are talking about taking advantage of SMP (?), the kernel is supposed to 
>do this automatically by balancing computations across all CPUs.
>Therefore, presumably, only the kernel would have to be compiled with any 
>additional effort.
>Except if I am missing something here, is the Wii's CPU instruction set 
>deviating from the Powerpc standard in some particular way that it would 
>require recompiling a whole program?

Here’s the explanation for the issues with SMP on the Wii U: 
https://gitlab.com/linux-wiiu/linux-wiiu/-/issues/20

It’s an issue with the Espresso CPU specifically.

-- Kurt

Re: Espresso (Nintendo Wii U) SMP build support

[Lennart Sorensen]

On Wed, Feb 26, 2025 at 10:49:36AM +, Athanasios Anastasiou wrote:
> Hi
> 
> I have noticed the same about the Wii and agree that it would be great to
> have Debian on it. But I can also see the point o
> 
> If we are talking about taking advantage of SMP (?), the kernel is supposed
> to do this automatically by balancing computations across all CPUs.
> Therefore, presumably, only the kernel would have to be compiled with any
> additional effort.
> Except if I am missing something here, is the Wii's CPU instruction set
> deviating from the Powerpc standard in some particular way that it would
> require recompiling a whole program?
> 
> Just out of curiosity, which instruction are you referring to in "...scan
> the existing binaries looking for the instruction..."?
> 
> All the best

Unfortunately it appears a mistake in the CPU means the instructions
used on powerpc for atomic locking don't work on the Wii due to it not
automatically synching caches between cores.  This means you can't fix it
in the kernel.  You literally need to make every piece of code using those
instructions insert a cache sync instruction before the atomic operation.
I guess Nintendo dealt with that in the compiler in the SDK for the Wii U,
so it wasn't really an issue there.

As a general purpose powerpc CPU, this thing could never have been
shipped in that state.  But it wasn't a general purpose powerpc CPU.

-- 
Len Sorensen

Re: Espresso (Nintendo Wii U) SMP build support

[Athanasios Anastasiou]

Hi

I have noticed the same about the Wii and agree that it would be great to
have Debian on it. But I can also see the point o

If we are talking about taking advantage of SMP (?), the kernel is supposed
to do this automatically by balancing computations across all CPUs.
Therefore, presumably, only the kernel would have to be compiled with any
additional effort.
Except if I am missing something here, is the Wii's CPU instruction set
deviating from the Powerpc standard in some particular way that it would
require recompiling a whole program?

Just out of curiosity, which instruction are you referring to in "...scan
the existing binaries looking for the instruction..."?

All the best

On Tue, Feb 25, 2025 at 11:26 PM Kurt Stine  wrote:

> On 2/25/25, 1:07 PM, "Lennart Sorensen"  > wrote:
> >Well someone would have to build and maintain it. It seems hard enough to
> >even get that for powerpc and ppc64, never mind a really niche platform.
>
> It would essentially be the same as the powerpc port, except that
> everything is compiled with the smp gcc patches. Everything built with the
> smp-patched GCC should also run fine on a non-Wii U PPC32 devices, so any
> test suites wouldn't have to change.
>
> >I wonder if there would be a way to scan the existing binaries looking
> >for the instruction to see if some packages might be able to be used
> >without rebuilding. Might not be very many though given probably any
> >code with threads in it would be affected.
>
> It's possible that some applications could work, but I doubt the effort of
> searching would be worth it.
>
> >I must admit today was the first time I had even heard of linux running
> >on the Wii U. I knew it had a powerpc chip in it, but I figured nintendo
> >likes to lock down their hardware.
>
> Linux was initially ported to the Wii U back in 2018. Nintendo does like
> to lock down their hardware, but that hasn't stopped people from hacking
> it. It just so happens that it's really simple to hack the Wii U to boot
> Linux on it. If you've got $30-40 and twenty minutes of free time, I
> recommend getting one and trying it out at some point :D
>
> -- Kurt
>
>