[libvirt] [RFC] exporting KVM host power saving capabilities through libvirt

[Dave Allan]

On Mon, Jul 04, 2011 at 10:00:20PM +0530, Vaidyanathan Srinivasan wrote:
> * Dave Allan <dallan at redhat.com> [2011-07-01 17:19:06]:
> 
> > On Fri, Jul 01, 2011 at 04:56:29PM -0400, Dave Allan wrote:
> > > On Tue, Jun 28, 2011 at 08:55:31PM +0530, Vaidyanathan Srinivasan wrote:
> > > > Hi,
> > > > 
> > > > Linux host systems running KVM support various power management
> > > > capabilities.  Most of the features like DVFS and sleep states can be
> > > > independently exploited by the host system itself based on system
> > > > utilisation subject to policies set by the administrator.
> > > > 
> > > > However, system-wide low power states like S3 and S4 would require
> > > > external communication and interaction with the systems management
> > > > stack in order to be used.  The first steps in this direction would be
> > > > to allow systems management stack to discover host power saving
> > > > capabilities like S3 and S4 along with various other host CPU
> > > > capabilities.
> > > > 
> > > > Libvirt seems to be the main glue layer between the platform and the
> > > > systems-management stack.  Adding host power savings capabilities as
> > > > part of libvirt host discovery mechanism seems to be one possible
> > > > approach without addition of any new APIs or agents.
> > > 
> > > Can you provide the use cases you're looking to address with this
> > > work?
> > 
> > BTW, I'm intrigued by what you might be doing here, but I don't feel
> > like I have enough information at this point to know quite what to
> > think of it.
> 
> Hi Dave,
> 
> Thanks for taking a look.  There are several advantages for using S3
> or S4 state for the host system instead power 'off' and 'on' for
> starting new guest instances.  The main advantage of discovering the
> capability through the systems management stack is to get the
> capability reported after checking against all policies and software
> compatibilities.  The overall idea is to allow high level systems
> management software that work through libvirt to discover and exploit
> these capabilities wherever possible.
> 
> Discovery of available power savings features is only the first step
> and I am looking for ideas to export these capabilities through
> libvirt.  I would expect the management stack that collects host
> capabilities would be keep these feature list and could use them to
> make various optimization decisions.

That certainly sounds useful to me.

Dave