On Thu, Sep 22, 2022 at 02:21:31PM -0700, Dave Hansen wrote:
> On 9/22/22 13:10, Andreas Mohr wrote:
> > (- but then what about other more modern chipsets?)
> >
> > --> we need to achieve (hopefully sufficiently precisely) a solution which
> > takes into account Zen3 STPCLK# improvements while
> > preserving "accepted" behaviour/requirements on *all* STPCLK#-hampered chipsets
> > ("STPCLK# I/O wait is default/traditional handling"?).
>
> Ideally, sure. But, we're talking about theoretically regressing the
> idle behavior of some indeterminate set of old systems, the majority of
> which are sitting in a puddle of capacitor goo at the bottom of a
> landfill right now. This is far from an ideal situation.
>
> FWIW, I'd much rather do something like
>
> if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) &&
> (boot_cpu_data.x86_model >= 0xF))
> return;
>
> inl(slow_whatever);
>
> than a Zen check. AMD has, as far as I know, been a lot more sequential
> and sane about model numbers than Intel, and there are some AMD model
> number range checks in the codebase today.
>
> A check like this would also be _relatively_ future-proof in the case
> that X86_FEATURE_ZEN stops getting set on future AMD CPUs. That's a lot
> more likely than AMD going and reusing a <0xF model.
Except you need to add VENDOR_HYGON at the very least. All of this turns
into a trainwreck real quick.
