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SubjectRe: [PATCH v3 2/3] x86: Remove vendor checks from prefer_mwait_c1_over_halt
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Hi, Wyes,

On Mon, 2022-05-23 at 21:19 +0530, Wyes Karny wrote:
> Hello Rui,
>
> On 5/20/2022 7:13 PM, Zhang Rui wrote:
> > On Thu, 2022-05-19 at 09:00 -0700, Dave Hansen wrote:
> > > On 5/10/22 03:18, Wyes Karny wrote:
> > > > static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86
> > > > *c)
> > > > {
> > > > + u32 eax, ebx, ecx, edx;
> > > > +
> > > > /* User has disallowed the use of MWAIT. Fallback to
> > > > HALT */
> > > > if (boot_option_idle_override == IDLE_NOMWAIT)
> > > > return 0;
> > > >
> > > > - if (c->x86_vendor != X86_VENDOR_INTEL)
> > > > + /* MWAIT is not supported on this platform. Fallback to
> > > > HALT */
> > > > + if (!cpu_has(c, X86_FEATURE_MWAIT))
> > > > return 0;
> >
> > I'm new to x86 code, a dumb question, what about the other vendors?
> > with this patch, prefer_mwait_c1_over_halt() can return 1 for other
> > vendors as well?
>
> This decision tree is based on cpuid features, so if the processor
> advertises MWAIT C1 support we would be choosing MWAIT.
> If any vendor wants to avoid choosing MWAIT (even cpuid shows MWAIT
> C1
> support), they can explicitly mention. Will add exceptions form them.
>
That's my concern.

This patch indeed changes the behaviors for vendors other than Intel
and AMD.
I don't know the impact of this, but just point out a behavior change
caused by this patch.

thanks,
rui

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