From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=40258 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OgMeN-0002Sx-KK for qemu-devel@nongnu.org; Tue, 03 Aug 2010 14:55:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OgMeM-00011I-2G for qemu-devel@nongnu.org; Tue, 03 Aug 2010 14:55:43 -0400 Received: from mail-qy0-f173.google.com ([209.85.216.173]:62002) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OgMeM-000117-00 for qemu-devel@nongnu.org; Tue, 03 Aug 2010 14:55:42 -0400 Received: by qyk35 with SMTP id 35so1171287qyk.4 for ; Tue, 03 Aug 2010 11:55:41 -0700 (PDT) Message-ID: <4C586627.7060907@codemonkey.ws> Date: Tue, 03 Aug 2010 13:55:35 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35? 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> <4C5854F1.3000905@codemonkey.ws> <4C5858B2.9090801@redhat.com> <4C585F5B.5070502@codemonkey.ws> <4C58635B.7020407@redhat.com> In-Reply-To: <4C58635B.7020407@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: kvm@vger.kernel.org, "Richard W.M. Jones" , Gleb Natapov , qemu-devel@nongnu.org On 08/03/2010 01:43 PM, Avi Kivity wrote: >> >> If Richard is willing to do the work to make -kernel perform faster >> in such a way that it fits into the overall mission of what we're >> building, then I see no reason to reject it. The criteria for >> evaluating a patch should only depend on how it affects other areas >> of qemu and whether it impacts overall usability. > > That's true, but extending fwcfg doesn't fit into the overall picture > well. We have well defined interfaces for pushing data into a guest: > virtio-serial (dma upload), virtio-blk (adds demand paging), and > virtio-p9fs (no image needed). Adapting libguestfs to use one of > these is a better move than adding yet another interface. On real hardware, there's an awful lot of interaction between the firmware and the platform. It's a pretty rich interface. On IBM systems, we actually extend that all the way down to userspace via a virtual USB RNDIS driver that you can use IPMI over. > A better (though still inaccurate) analogy is would be if the > developers of a guest OS came up with a virtual bus for devices and > were willing to do the work to make this bus perform better. Would we > accept this new work or would we point them at our existing bus (pci) > instead? Doesn't this precisely describe virtio-s390? > > Really, the bar on new interfaces (both to guest and host) should be > high, much higher than it is now. Interfaces should be well > documented, future proof, migration safe, and orthogonal to existing > interfaces. Okay, but this is a bigger discussion that I'm very eager to have. But we shouldn't explicitly apply new policies to random patches without clearly stating the policy up front. Regards, Anthony Liguori > While the first three points could be improved with some effort, > adding a new dma interface is not going to be orthogonal to virtio. > And frankly, libguestfs is better off switching to one of the other > interfaces. Slurping huge initrds isn't the right way to do this. > >> As a side note, we ought to do a better job of removing features that >> have created a burden on other areas of qemu that aren't actively >> being maintained. That's a different discussion though. > > Sure, we need something like Linux' > Documentation/feature-removal-schedule.txt for people to ignore. >