Re: [PATCH 15/15] x86/atomics: Remove !CONFIG_X86_CX8 methods

[Ingo Molnar <mingo@kernel.org>]

* Brian Gerst <brgerst@gmail.com> wrote:

> On Fri, Apr 25, 2025 at 10:30 AM Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> >
> >
> > On 25. 04. 25 10:42, Ingo Molnar wrote:
> >
> > > -#endif
> > > +#define arch_cmpxchg64                       __cmpxchg64
> > > +#define arch_cmpxchg64_local         __cmpxchg64_local
> > > +#define arch_try_cmpxchg64           __try_cmpxchg64
> > > +#define arch_try_cmpxchg64_local     __try_cmpxchg64_local
> > >
> > >   #define system_has_cmpxchg64()              boot_cpu_has(X86_FEATURE_CX8)
> >
> > #define system_has_cmpxchg64()          1
> 
> Or just outright removed, since x86 was the only arch that defined it.

No, it cannot be removed, x86-32 *is* still the only 32-bit arch that 
enables it.

I.e. defining it to 1 is the correct solution, and that unconditionally 
enables the SLUB code optimizations. It depended on a runtime 
boot_cpu_has() check before.

Removing it would remove the optimization from x86-32 for no good 
reason.

Thanks,

	Ingo