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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date: Tue, 12 Mar 2024 10:16:10 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, x86-ml <x86@kernel.org>,
	lkml <linux-kernel@vger.kernel.org>,
	linux-edac <linux-edac@vger.kernel.org>
Subject: Re: [GIT PULL] EDAC updates for v6.9
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* Borislav Petkov <bp@alien8.de> wrote:

> On Mon, Mar 11, 2024 at 06:12:54PM -0700, Linus Torvalds wrote:
> > Ho humm. Lookie here:
> > 
> >     static inline unsigned int topology_amd_nodes_per_pkg(void)
> >     { return 0; };
> > 
> > that's the UP case.
> > 
> > Yeah, I'm assuming nobody tests this for UP,
> 
> Unless it gets randomly enabled in my randconfig builds once in a blue
> moon, I'd say pretty seldomly. I've heard people raise the question
> multiple times whether we should simply make CONFIG_SMP default y on x86
> and frankly, it'll get rid of a whole bunch of stupid corner cases like
> that...

Making it 'default y' in the Kconfig alone changes very little, as people & 
bots will still stumble on !SMP via allnoconfig or randconfig builds.

If you mean forcing CONFIG_SMP via 'select SMP' on x86 on the other hand, 
that's worth considering - although I think there will be a ton of extra 
cross-build breakage as most patches still get created & tested on x86.

In other words, the x86 UP build basically has the side-effect utility of 
covering a lot of UP cross-build scenarios in generic code.

I think the most viable approach would be to make SMP the only model all 
across the kernel (and eventually removing the CONFIG_SMP option), while 
propagating UP data structures and locking primitives to the UP arch level, 
instead of having CONFIG_SMP #ifdefs in generic code.

Maybe not today, but certainly in a few years.

Thanks,

	Ingo