Re: [Xen-devel] Re: [GIT PULL] Xen APIC hooks (with io_apic_ops)

From: Ingo Molnar
Date: Wed May 27 2009 - 20:15:21 EST

* Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> wrote:

> > The Linux scheduler already supports multiple scheduling
> > classes. If we find that none of them will fit our needs, we'll
> > propose a new one. When the need can be demonstrated to be
> > real, and the implementation can be clean, Linux can usually be
> > adapted.
> But that's exactly George and Jeremy's point. KVM will eventually
> require changes that clutter Linux for purposes that are relevant
> only to a hypervisor.

That's wrong. Any such scheduler classes would also help: control
groups, containers, vserver, UML and who knows what other isolation
project. Many of such mechanisms are already implemented as well.

I rarely see any KVM-only feature in generic kernel code, and that's

Xen changes - especially dom0 - are overwhelmingly not about
improving Linux, but about having some special hook and extra
treatment in random places - and that's really bad.

I also find it pretty telling that you cut out the most important
point of Avi's reply:

> > I think the Xen design has merit if it can truly make dom0 a
> > guest -- that is, if it can survive dom0 failure. Until then,
> > you're just taking a large interdependent codebase and splitting
> > it at some random point, but you don't get any stability or
> > security in return.

that crucial question really has to be answered honestly and

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