RE: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD systems

From	"Ghannam, Yazen" <Yazen.Ghannam@amd.com>
Newsgroups	linux.kernel
Subject	RE: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD systems
Date	2017-05-23 15:00 +0200
Message-ID	<tKhzP-3jV-13@gated-at.bofh.it> (permalink)
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> -----Original Message-----
> From: Borislav Petkov [mailto:bp@alien8.de]
> Sent: Tuesday, May 23, 2017 3:59 AM
> To: Ghannam, Yazen <Yazen.Ghannam@amd.com>
> Cc: linux-pm@vger.kernel.org; x86@kernel.org; linux-
> kernel@vger.kernel.org; rjw@rjwysocki.net; len.brown@intel.com;
> pavel@ucw.cz
> Subject: Re: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on
> AMD systems
> 
> On Mon, May 22, 2017 at 08:20:56PM +0000, Ghannam, Yazen wrote:
> > On the other hand, MWAIT on AMD limits the hardware to using only
> > certain, shallower Cstates. This is okay if we define individual
> > states and use MWAIT for some of them. But it would consume more
> power if used always.
> 
> Let me see if I understand it correctly:
> 
> Even though we used to do HLT on previous families as idling with HLT
> *is* the preferred method until now, with your change you're moving
> *every* AMD machine out there to do MWAIT now.
> 

No, AMD systems will continue to use HLT unless the BIOS specifies the
use of MWAIT using a FFH entry in the ACPI _CST.

All this change does is *allow* us to use MWAIT through the FFH
implementation if the BIOS defines it. It doesn't *force* a change.

If the BIOS doesn't define the appropriate _CST entry or it defines it
wrong, then we'll fallback to using HLT.

Thanks,
Yazen

Thread

Re: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD  systems Borislav Petkov <bp@alien8.de> - 2017-05-22 18:30 +0200
  RE: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD  systems "Ghannam, Yazen" <Yazen.Ghannam@amd.com> - 2017-05-22 22:30 +0200
    Re: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD  systems Borislav Petkov <bp@alien8.de> - 2017-05-23 10:00 +0200
      RE: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD  systems "Ghannam, Yazen" <Yazen.Ghannam@amd.com> - 2017-05-23 15:00 +0200
        Re: [PATCH] x86/ACPI/cstate: Allow ACPI C1 FFH MWAIT use on AMD  systems Borislav Petkov <bp@alien8.de> - 2017-05-23 15:10 +0200

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