linux-kernel - Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side

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Date:	Tue, 16 Mar 2010 17:35:37 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	oerg Roedel <joro@...tes.org>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, ziteng.huang@...el.com
Subject: Re: [PATCH] Enhance perf to collect KVM guest os statistics from
 host side


* Frank Ch. Eigler <fche@...hat.com> wrote:

> Hi -
> 
> On Tue, Mar 16, 2010 at 04:52:21PM +0100, Ingo Molnar wrote:
> > [...]
> > > Perhaps the fact that kvm happens to deal with an interesting application 
> > > area (virtualization) is misleading here.  As far as the host kernel or 
> > > other host userspace is concerned, qemu is just some random unprivileged 
> > > userspace program [...]
> 
> > You are quite mistaken: KVM isnt really a 'random unprivileged
> > application' in this context, it is clearly an extension of
> > system/kernel services.
> 
> I don't know what "extension of system/kernel services" means in this 
> context, beyond something running on the system/kernel, like every other 
> process. [...]

It means something like my example of 'extended to guest space' 
/proc/kallsyms:

> > [...]
> >
> > ( Which can be seen from the simple fact that what started the
> >   discussion was 'how do we get /proc/kallsyms from the guest'. I.e. an 
> >   extension of the existing host-space /proc/kallsyms was desired. )
> 
> (Sorry, that smacks of circular reasoning.)

To me it sounds like an example supporting my point. /proc/kallsyms is a 
service by the kernel, and 'perf kvm' desires this to be extended to guest 
space as well.

Thanks,

	Ingo
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