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Message-ID: <20090528001350.GD26820@elte.hu>
Date: Thu, 28 May 2009 02:13:50 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Dan Magenheimer <dan.magenheimer@...cle.com>
Cc: Avi Kivity <avi@...hat.com>,
George Dunlap <George.Dunlap@...citrix.com>,
Jeremy Fitzhardinge <jeremy@...p.org>,
Xen-devel <xen-devel@...ts.xensource.com>,
the arch/x86 maintainers <x86@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Keir Fraser <keir.fraser@...citrix.com>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Xen-devel] Re: [GIT PULL] Xen APIC hooks (with io_apic_ops)
* Dan Magenheimer <dan.magenheimer@...cle.com> 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
good.
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
upfront.
Ingo
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