From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35? Date: Tue, 03 Aug 2010 12:42:09 -0500 Message-ID: <4C5854F1.3000905@codemonkey.ws> References: <20100803111306.GA21886@amd.home.annexia.org> <20100803113302.GT24773@redhat.com> <20100803121000.GV13789@amd.home.annexia.org> <20100803123714.GU24773@redhat.com> <20100803124808.GW13789@amd.home.annexia.org> <4C58176B.2050306@redhat.com> <20100803140506.GD22211@amd.home.annexia.org> <4C5829E1.60004@redhat.com> <20100803145337.GF22211@amd.home.annexia.org> <4C583F6A.7030600@redhat.com> <20100803162857.GX13789@amd.home.annexia.org> <4C584781.9040609@redhat.com> <4C5847CD.9080107@codemonkey.ws> <4C5848C7.3090806@redhat.com> <4C584982.5000108@codemonkey.ws> <4C584B66.5070404@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Richard W.M. Jones" , qemu-devel@nongnu.org, Gleb Natapov , kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mail-qy0-f174.google.com ([209.85.216.174]:50929 "EHLO mail-qy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756521Ab0HCRmP (ORCPT ); Tue, 3 Aug 2010 13:42:15 -0400 Received: by qyk7 with SMTP id 7so361754qyk.19 for ; Tue, 03 Aug 2010 10:42:14 -0700 (PDT) In-Reply-To: <4C584B66.5070404@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 08/03/2010 12:01 PM, Avi Kivity wrote: >> You mean, only one class of users cares about the performance of >> loading an initrd. However, you've also argued in other threads how >> important it is not to break libvirt even if it means we have to do >> silly things (like change help text). >> >> So... why is it that libguestfs has to change itself and yet we >> should bend over backwards so libvirt doesn't have to change itself? > > > libvirt is a major user that is widely deployed, and would be > completely broken if we change -help. Changing -help is of no > consequence to us. > libguestfs is a (pardon me) minor user that is not widely used, and > would suffer a performance regression, not total breakage, unless we > add a fw-dma interface. Adding the interface is of consequence to us: > we have to implement live migration and backwards compatibility, and > support this new interface for a long while. I certainly buy the argument about making changes of little consequence to us vs. ones that we have to be concerned about long term. However, I don't think we can objectively differentiate between a "major" and "minor" user. Generally speaking, I would rather that we not take the position of "you are a minor user therefore we're not going to accommodate you". Regards, Anthony Liguori > > In an ideal world we wouldn't tolerate any regression. The world is > not ideal, so we prioritize. > > the -help change scores very high on benfit/cost. fw-dma, much lower. > > Note in both cases the long term solution is for the user to move to > another interface (cap reporting, virtio), so adding an interface > which would only be abandoned later by its only user drops the > benfit/cost ratio even further. >