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

Vaidyanathan Srinivasan svaidy at linux.vnet.ibm.com
Mon Jul 4 16:30:20 UTC 2011

* 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.


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