Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play_dead()

[Wysocki, Rafael J]

On 11/13/2024 5:22 PM, Peter Zijlstra wrote:
> On Wed, Nov 13, 2024 at 05:11:38PM +0530, Gautham R. Shenoy wrote:
>
> > How about something like this (completely untested)
> >
> > ---------------------x8----------------------------------------------------
> >
> > diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> > index f3ffd0a3a012..bd611771fa6c 100644
> > --- a/arch/x86/kernel/acpi/cstate.c
> > +++ b/arch/x86/kernel/acpi/cstate.c
> > @@ -215,6 +215,24 @@ void __cpuidle acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cx)
> >   }
> >   EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_enter);
> >   
> > +static int acpi_processor_ffh_play_dead(struct acpi_processor_cx *cx)
> > +{
> > +       unsigned int cpu = smp_processor_id();
> > +       struct cstate_entry *percpu_entry;
> > +
> > +       /*
> > +        * This is ugly. But AMD processors don't prefer MWAIT based
> > +        * C-states when processors are offlined.
> > +        */
> > +       if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
> > +           boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
> > +               return -ENODEV;
> Are there AMD systems with FFh idle states at all?

I don't know.


> Also, I don't think this works right, the loop in cpuidle_play_dead()
> will terminate on this, and not try a shallower state which might have
> IO/HLT on.

I think you are right.


> > +
> > +       percpu_entry = per_cpu_ptr(cpu_cstate_entry, cpu);
> > +       return mwait_play_dead_with_hints(percpu_entry->states[cx->index].eax);
> > +}
> > +EXPORT_SYMBOL_GPL(acpi_processor_ffh_play_dead);