linux-kernel - Re: [ANNOUNCE] Native Linux KVM tool

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Message-ID: <4D9EBBC3.2040803@siemens.com>
Date:	Fri, 08 Apr 2011 09:39:47 +0200
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Anthony Liguori <anthony@...emonkey.ws>,
	Ingo Molnar <mingo@...e.hu>, Avi Kivity <avi@...hat.com>,
	linux-kernel@...r.kernel.org, aarcange@...hat.com,
	mtosatti@...hat.com, kvm@...r.kernel.org, joro@...tes.org,
	penberg@...helsinki.fi, asias.hejun@...il.com, gorcunov@...il.com
Subject: Re: [ANNOUNCE] Native Linux KVM tool

On 2011-04-08 07:14, Pekka Enberg wrote:
> Hi Anthony,
> 
> On Fri, Apr 8, 2011 at 5:14 AM, Anthony Liguori <anthony@...emonkey.ws> wrote:
>> If someone was going to seriously go about doing something like this, a
>> better approach would be to start with QEMU and remove anything non-x86 and
>> all of the UI/command line/management bits and start there.
>>
>> There's nothing more I'd like to see than a viable alternative to QEMU but
>> ignoring any of the architectural mistakes in QEMU and repeating them in a
>> new project isn't going to get there.
> 
> Hey, feel free to help out! ;-)
> 
> I don't agree that a working 2500 LOC program is 'repeating the same
> architectural mistakes' as QEMU. I hope you realize that we've gotten
> here with just three part-time hackers working from their proverbial
> basements. So what you call mistakes, we call features for the sake of
> simplicity.
> 
> I also don't agree with this sentiment that unless we have SMP,
> migration, yadda yadda yadda, now, it's impossible to change that in
> the future. It ignores the fact that this is exactly how the Linux
> kernel evolved and the fact that we're aggressively trying to keep the
> code size as small and tidy as possible so that changing things is as
> easy as possible.

I agree that it's easy to change 2kSomething LOC for this. But if you
now wait too long designing in essential features like SMP, a scalable
execution model, and - very important - portability (*), it can get
fairly painful to fix such architectural deficits later on. How long did
it take for Linux to overcome the BKL? QEMU is in the same unfortunate
position.

Jan

(*) I would consider Anthony's idea to drop anything !=x86 a mistake
given where KVM is moving to, today on PPC, tomorrow likely on ARM -
just to name two examples.

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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