Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors based on the Zen microarchitecture

[Rafael J. Wysocki]

On Thu, Sep 22, 2022 at 10:17 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Wed, Sep 21, 2022 at 09:48:13PM +0200, Borislav Petkov wrote:
> > On Wed, Sep 21, 2022 at 05:00:35PM +0200, Peter Zijlstra wrote:
> > > On Wed, Sep 21, 2022 at 12:06:38PM +0530, K Prateek Nayak wrote:
> > > > Processors based on the Zen microarchitecture support IOPORT based deeper
> > > > C-states.
> > >
> > > I've just gotta ask; why the heck are you using IO port based idle
> > > states in 2022 ?!?! You have have MWAIT, right?
> >
> > They have both. And both is Intel technology. And as I'm sure you
> > know AMD can't do their own thing - they kinda have to follow Intel.
> > Unfortunately.
> >
> > Are you saying modern Intel chipsets don't do IO-based C-states anymore?
>
> I've no idea what they do, but Linux exclusively uses MWAIT on Intel as
> per intel_idle.c.

Well, it can be forced to use ACPI idle instead.

> MWAIT also cuts down on IPIs because it wakes from the TIF write.

Right.