linux-kernel - Re: [RFC] Unify KVM kernel-space and user-space code into a single project

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Date:	Sun, 21 Mar 2010 21:37:04 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	Olivier Galibert <galibert@...ox.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"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,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Fr?d?ric Weisbecker <fweisbec@...il.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
 project


* Avi Kivity <avi@...hat.com> wrote:

> On 03/21/2010 10:08 PM, Olivier Galibert wrote:
> >On Sun, Mar 21, 2010 at 10:01:51PM +0200, Avi Kivity wrote:
> >>On 03/21/2010 09:17 PM, Ingo Molnar wrote:
> >>>Adding any new daemon to an existing guest is a deployment and usability
> >>>nightmare.
> >>>
> >>The logical conclusion of that is that everything should be built into
> >>the kernel.  Where a failure brings the system down or worse.  Where you
> >>have to bear the memory footprint whether you ever use the functionality
> >>or not.  Where to update the functionality you need to deploy a new
> >>kernel (possibly introducing unrelated bugs) and reboot.
> >>
> >>If userspace daemons are such a deployment and usability nightmare,
> >>maybe we should fix that instead.
> >Which userspace?  Deploying *anything* in the guest can be a
> >nightmare, including paravirt drivers if you don't have a natively
> >supported in the OS virtual hardware backoff.
> 
> That includes the guest kernel.  If you can deploy a new kernel in the 
> guest, presumably you can deploy a userspace package.

Note that with perf we can instrument the guest with zero guest-kernel 
modifications as well.

We try to reduce the guest impact to a bare minimum, as the difficulties in 
deployment are function of the cross section surface to the guest.

Also, note that the kernel is special with regards to instrumentation: since 
this is the kernel project, we are doing kernel space changes, as we are doing 
them _anyway_. So adding symbol resolution capabilities would be a minimal 
addition to that - while adding a while new guest package for the demon would 
significantly increase the cross section surface.

	Ingo
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