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

[Ingo Molnar <mingo@elte.hu>]

* Pekka Enberg <penberg@cs.helsinki.fi> wrote:

> Hi Avi,
> 
> On Mon, Mar 22, 2010 at 2:49 PM, Avi Kivity <avi@redhat.com> wrote:
> > Seems like perf is also split, with sysprof being developed outside the
> > kernel. ?Will you bring sysprof into the kernel? ?Will every feature be
> > duplicated in prof and sysprof?
> 
> I am glad you brought it up! Sysprof was historically outside of the kernel 
> (with it's own kernel module, actually). While the GUI was nice, it was much 
> harder to set up compared to oprofile so it wasn't all that popular. Things 
> improved slightly when Ingo merged the custom kernel module but the 
> _userspace_ part of sysprof was lagging behind a bit. I don't know what's 
> the situation now that they've switched over to perf syscalls but you 
> probably get my point.
> 
> It would be nice if the two projects merged but I honestly don't see any 
> fundamental problem with two (or more) co-existing projects. Friendly 
> competition will ultimately benefit the users (think KDE and Gnome here).

See my previous mail - what i see as the most healthy project model is to have 
a full solution reference implementation, connected to a flexible halo of 
plugins or sub-apps.

Firefox does that, KDE does that, and Gnome as well to a certain degree.

The 'halo' provides a constant feedback of new features, and it also provides 
competition and pressure on the 'main' code to be top-notch.

The problem i see with KVM is that there's no reference implementation! There 
is _only_ the KVM kernel part which is not functional in itself. Surrounded by 
a 'halo' - where none of the entities is really 'the' reference implementation 
we call 'KVM'.

This causes constant quality problems as the developers of the main project 
dont have constant pressure towards good quality (it is not their 
responsibility to care about user-space bits after all), plus it causes a lack 
of focus as well: integration between (friendly) competing user-space 
components is a lot harder than integration within a single framework such as 
Firefox.

I hope this explains my points about modularization a bit better! I suggested 
KVM to grow a user-space tool component in the kernel repo in tools/kvm/, 
which would become the reference implementation for tooling. User-space 
projects can still provide alternative tooling or can plug into this tooling, 
just like they are doing it now. So the main effect isnt even on those 
projects but on the kernel developers. The ABI remains and all the user-space 
packages and projects remain.

Yes, i thought Qemu would be a prime candidate to be the baseline for 
tools/kvm/, but i guess that has become socially impossible now after this 
flamewar. It's not a big problem in the big scheme of things: tools/kvm/ is 
best grown up from a small towards larger size anyway ...

Thanks,
 
	Ingo