Re: [PATCH 0/11] VMI / Paravirt bugfixes for 2.6.21

[Zachary Amsden]

Arjan van de Ven wrote:
> On Tue, 2007-02-06 at 16:11 +1100, Rusty Russell wrote:
>   
> > On Mon, 2007-02-05 at 20:54 -0800, Zachary Amsden wrote:
> >     
> > > Rusty Russell wrote:
> > >       
> > > > Indeed, I'm expecting to push lguest this week, and this code will
> > > > effect me, so I'd like to see this in a -mm soon...
> > > >         
> > > Yes, I took a look at the lguest changes today and I think these won't 
> > > generate conflicts, just make stuff easier for you ;)  Course you've now 
> > > got a couple new paravirt-ops to support, but the native ones are fine 
> > > for temporary use.
> > >       
> > Implementing stolen time is something I'd like to do, since it'd be a
> > nice self-contained example the expectations.
> >     
>
>
> hmm stolen time could even be useful without virtualization; to a large
> degree, if cpufreq reduces the speed of your cpu you have "stolen
> cycles" that way... I wonder if this concept can be used for that as
> well...
>   

Yes, stolen time happens in most moderns systems as a result of power 
management (and you can probably count SMM cycles as stolen if only 
there was a way to count them).  It would be useful to report on a 
laptop, for instance, how many cycles have been stolen by running off 
battery or on a server because of heat issues.  Having an interface for 
Linux to report this seems useful.  It is a covert channel, however, in 
a virtualized environment, so there should be some provision in the 
hypervisor to turn it off.

Zach
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