Re: [Qemu-devel] [RFC PATCH 3/4] pc: acpi: add _CST support

[Michael S. Tsirkin]

On Thu, Aug 09, 2018 at 12:00:11PM +0200, Igor Mammedov wrote:
> On Wed, 8 Aug 2018 23:17:48 +0300
> "Michael S. Tsirkin" <address@hidden> wrote:
> 
> > On Wed, Aug 08, 2018 at 05:15:48PM +0200, Igor Mammedov wrote:
> > > Reuse CPU hotplug IO registers for passing a CST entry
> > > containing package for shalowest C1 using mwait and
> > > read it out in guest with new CCST AML method.  
> > 
> > I don't see how 1 entry is enough. We need to describe full _CST package so
> > that guest can do reasonable power management on the CPU.
> I was assuming that CST are to be used for mwait/monitor idle combo
> to help reduce latencies/vmexits on cpus wakeup from idle state, hence 1 
> entry.
> It's trivial to add as much as needed entries though.
> If you are fine with approach I can respin patch with arbitrary
> number of CStates.

You will find that the code then becomes very messy, and
dynamic size of the package is one of the things
that makes it messy.


> > > The CState support is optional and could be turned on
> > > with '-global PIIX4_PM.cstate=on' CLI option.
> > > 
> > > Signed-off-by: Igor Mammedov <address@hidden>
> > > ---
> [...]