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

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 10 Aug 2018 02:01:00 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> 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" <mst@redhat.com> 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.
it turned up like extra ~10LOC, for a loop based impl.
I'll post amended patch here as reply with full update series in my repo.


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