RE: [Xen-devel] expose MWAIT to dom0

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 15.08.11 at 10:09, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>>  From: Jan Beulich [mailto:JBeulich@xxxxxxxxxx] 
>> >>> On 15.08.11 at 07:35, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>> > It's unlikely to make into upstream, and also get lost in
>> > into some distro such as SLES11.
>> 
>> We can certainly fix it there.
>> 
> 
> that'd be great. I/O method has observable impact on power efficiency,
> and the fix would be very welcomed. :-)

While the change is simple to do and works, I'm somewhat concerned
that while improving the situation on CPUs that support the break-on-
interrupt extension to mwait, it would result in C2/C3 not being usable
at all on CPUs that don't (but support mwait in its simpler form and
have ACPI tables specifying FFH as address space id). Is that only a
theoretical concern (i.e. is there an implicit guarantee that for other
than C1 FFH wouldn't be specified without that extension being
available)? I thinks it's a practical one, or otherwise there wouldn't
be a point in removing the ACPI_PDC_C_C2C3_FFH bit prior to _PDC
evaluation.

Jan


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