Re: [Xen-devel] [PATCH 0/3] mwait support for AMD processors

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.02.19 at 21:23, <Brian.Woods@xxxxxxx> wrote:
> This patch series add support and enablement for mwait on AMD Naples
> and Rome processors.  Newer AMD processors support mwait, but only for
> c1, and for c2 halt is used.  The mwait-idle driver is modified to be
> able to use both mwait and halt for idling.

I recall you saying so elsewhere, but I continue to be confused. Afaik
HLT is specified to mean C1. Without having looked at the patches,
I'm also not happy to see you say you make the driver capable of using
HLT. That's not its purpose, and I think the ACPI driver should instead
be used for that.

It is my understanding that the driver is there solely to overcome
recurring issues with BIOSes not providing optimal (or even correct)
ACPI tables. Since for C1 we don't even need any ACPI tables (we
enter C1 [through HLT] whenever no other C states are defined),
I'm having trouble seeing what problem would be addressed here.
Are there really no deeper C states than C2 supported by your CPUs?

Jan



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