Re: [Xen-devel] [PATCH 3/3] mwait-idle: add enablement for AMD Naples and Rome

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.03.19 at 16:59, <Brian.Woods@xxxxxxx> wrote:
> On 3/15/19 3:54 AM, Jan Beulich wrote:
>>>>> On 14.03.19 at 20:29, <Brian.Woods@xxxxxxx> wrote:
>>> There's another register we _might_
>>> be able to use, but support for CC6 is AND'd with that and another
>>> another register (we don't have access to). The register we'd read is
>>> also RW.  So I'm not sure I trust it.
>> 
>> It's hard to believe that one can't find out whether HLT would enter
>> only CC1 or eventually also CC6.
> 
> There's a register, but it's AND'd with firmware for if C6 is enabled. 
> Assuming it isn't touched, it should be able to determine if C6 is 
> enabled or not by BIOS.  That leads to more code and the negative of not 
> checking is system thinking it's using CC6 when it's really using CC1. 
> It's also NDA'd so I'd have to get approval to use it (and then also put 
> it in the public PPR).

Well, no need to go through too many hoops for this. It would
just have been nice to tell the two apart, not the least because
of their quite different wakeup latencies.

Jan



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