From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: Need a new plan on adding kvm support to qemu Date: Tue, 26 May 2009 03:31:40 -0500 Message-ID: <4A1BA8EC.9080803@codemonkey.ws> References: <4A1AB196.10008@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Jan Kiszka , qemu-devel , KVM list To: Avi Kivity Return-path: Received: from mail-gx0-f166.google.com ([209.85.217.166]:34373 "EHLO mail-gx0-f166.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753079AbZEZIbn (ORCPT ); Tue, 26 May 2009 04:31:43 -0400 Received: by gxk10 with SMTP id 10so6362393gxk.13 for ; Tue, 26 May 2009 01:31:44 -0700 (PDT) In-Reply-To: <4A1AB196.10008@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > While I appreciate the efforts to add clean qemu/kvm integration in > upstream, it's driving me mad. > > Every merge I'm faced with regressions (mostly due to changing code, > not to upstream breakage) and need to fix things. Work done during > merges is very likely to contain errors since there's no incremental > change to review and test. > > We now have two very different kvm implementations: > > The upstream implementation: > > - mostly clean > - crippled > - no smp > - no kernel irqchip > - no kernel pit > - no device assignment > - reduced support for older host kernels > - no ia64 support > - no nmi support > - no tpr patching > - almost totally untested (small userbase) > > The downstream implementation: > - a tangled mess > - featureful and performant > #include > - heavily tested (kvm-autotest, large kvm userbase, inclusion in distros) > > What we have here is the classic rewrite fallacy (rewriting from > scratch is easier than fixing, now six months into the voyage with no > end in sight) coupled with inflicting pain to the largest contributor > to qemu (I mean the kvm community, not me personally). Meanwhile, new > kvm kernel features need to be implemented twice in userspace. > > I propose that we stop this. It is fragmenting the development > effort, causing regressions (again, mostly through merge issues, but > also through new code duplicating old code incorrectly), and not > really helping upstream qemu. It's also the first case I've heard of > where a project competes with itself (well not really but it's a nice > soundbite). > > As a first step I've merged a copy of libkvm into qemu linkage (i.e. > not as a library), so we can start to use the upstream code (say, use > kvm_ioctl() from libkvm.c). It's not going to be easy, but what we > have now isn't working. I'm with you. I think at this point we should try to make the qemu-kvm code use the upstream QEMU code where ever possible and then refactor the qemu-kvm into a mergable state. A good second step would be getting rid of libkvm entirely. Regards, Anthony Liguori