> -----Original Message----- > From: Borislav Petkov [mailto:[email protected]] > Sent: Tuesday, May 23, 2017 3:59 AM > To: Ghannam, Yazen <[email protected]> > Cc: [email protected]; [email protected]; linux- > [email protected]; [email protected]; [email protected]; > [email protected] > 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
