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

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Date:	Thu, 18 Mar 2010 11:28:03 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	Anthony Liguori <anthony@...emonkey.ws>,
	"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 03/18/2010 10:56 AM, Ingo Molnar wrote:
> >* Avi Kivity<avi@...hat.com>  wrote:
> >
> >>On 03/17/2010 10:10 AM, Ingo Molnar wrote:
> >>>>It's about who owns the user interface.
> >>>>
> >>>>If qemu owns the user interface, than we can satisfy this in a very
> >>>>simple way by adding a perf monitor command.  If we have to support third
> >>>>party tools, then it significantly complicates things.
> >>>Of course illogical modularization complicates things 'significantly'.
> >>Who should own the user interface then?
> >If qemu was in tools/kvm/ then we wouldnt have such issues. A single patch (or
> >series of patches) could modify tools/kvm/, arch/x86/kvm/, virt/ and
> >tools/perf/.
> 
> We would have exactly the same issues, only they would be in a single 
> repository.  The only difference is that we could ignore potential 
> alternatives to qemu, libvirt, and RHEV-M.  But that's not how kernel ABIs 
> are developed, we try to make them general, not suited to just one consumer 
> that happens to be close to our heart.

Not at all - as i replied to in a previous mail, tools/perf/ still has a clear 
userspace interface and ABI, and external projects are making use of it.

So there's no problem with the ABI at all.

In fact our experience has been the opposite: the perf ABI is markedly better 
_because_ there's an immediate consumer of it in the form of tools/perf/. It 
gets tested better and external projects can get their ABI tweaks in as well 
and can provide a reference implementation for tools/perf. This has happened a 
couple of times. It's a win-win scenario.

So the exact opposite of what you suggest is happening in practice.

Thanks,

	Ingo
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