From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joerg Roedel <joro@8bytes.org>
Subject: Re: KVM PMU virtualization
Date: Fri, 26 Feb 2010 11:42:18 +0100
Message-ID: <20100226104218.GE4246@8bytes.org>
References: <4B86917C.4070102@redhat.com> <20100225173423.GB4246@8bytes.org> <1267152917.1726.82.camel@localhost> <20100226085105.GC4246@8bytes.org> <20100226091732.GI15885@elte.hu>
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Cc: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
	Jes Sorensen <Jes.Sorensen@redhat.com>,
	KVM General <kvm@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Avi Kivity <avi@redhat.com>,
	Zachary Amsden <zamsden@redhat.com>,
	Gleb Natapov <gleb@redhat.com>, ming.m.lin@intel.com
To: Ingo Molnar <mingo@elte.hu>
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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