Re: KVM PMU virtualization

[Joerg Roedel <joro@8bytes.org>]

On Fri, Feb 26, 2010 at 10:17:32AM +0100, Ingo Molnar wrote:
> My suggestion, as always, would be to start very simple and very minimal:
> 
> Enable 'perf kvm top' to show guest overhead. Use the exact same kernel image 
> both as a host and as guest (for testing), to not have to deal with the symbol 
> space transport problem initially. Enable 'perf kvm record' to only record 
> guest events by default. Etc.
> 
> This alone will be a quite useful result already - and gives a basis for 
> further work. No need to spend months to do the big grand design straight 
> away, all of this can be done gradually and in the order of usefulness - and 
> you'll always have something that actually works (and helps your other KVM 
> projects) along the way.
> 
> [ And, as so often, once you walk that path, that grand scheme you are 
>   thinking about right now might easily become last year's really bad idea ;-) ]
> 
> So please start walking the path and experience the challenges first-hand.

That sounds like a good approach for the 'measure-guest-from-host'
problem. It is also not very hard to implement. Where does perf fetch
the rip of the nmi from, stack only or is this configurable?

	Joerg