From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [Qemu-devel] [PATCH] kvm: Set default accelerator to "kvm" if the host supports it Date: Mon, 01 Oct 2012 14:03:54 -0500 Message-ID: <87626u9fqd.fsf@codemonkey.ws> References: <20120930191146.GA20012@amt.cnet> <50694EC1.8060006@siemens.com> <20121001093102.GA14797@amt.cnet> <50696E9E.7030302@siemens.com> <87zk468h3y.fsf@codemonkey.ws> <50699CDC.1010604@redhat.com> <87wqzap9ui.fsf@codemonkey.ws> <5069A9DF.4040606@siemens.com> <5069C814.7010201@suse.de> <20121001164730.GC15554@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Jan Kiszka , kvm , Scott Moser , Marcelo Tosatti , Michael Tokarev , qemu-devel , Bruce Rogers , Avi Kivity , Cole Robinson , Paolo Bonzini To: "Daniel P. Berrange" , Andreas =?utf-8?Q?F=C3=A4r?= =?utf-8?Q?ber?= Return-path: Received: from mail-oa0-f46.google.com ([209.85.219.46]:33793 "EHLO mail-oa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750768Ab2JATD7 convert rfc822-to-8bit (ORCPT ); Mon, 1 Oct 2012 15:03:59 -0400 Received: by oagh16 with SMTP id h16so5423263oag.19 for ; Mon, 01 Oct 2012 12:03:58 -0700 (PDT) In-Reply-To: <20121001164730.GC15554@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: "Daniel P. Berrange" writes: > On Mon, Oct 01, 2012 at 06:43:00PM +0200, Andreas F=C3=A4rber wrote: >> Hello Jan, >>=20 >> Am 01.10.2012 16:34, schrieb Jan Kiszka: >> > If we built a target for a host that supports KVM in principle, se= t the >> > default accelerator to KVM as well. This also means the start of Q= EMU >> > will fail to start if KVM support turns out to be unavailable at >> > runtime. >>=20 >> From a distro point of view this of course means that we will build >> against KVM and that the new KVM default will start to fail for user= s on >> very old hardware. Can't we do a runtime check to select the default= ? > > NB, this is *not* only about old hardware. There are plenty of users = who > use QEMU inside VMs. One very common usage I know of is image buildin= g > tools which are run inside Amazon VMs, using libguestfs & QEMU. But libguest can set it's accelerator option to whatever it wants. If your running QEMU under a VM, it's pretty reasonable to have to use = a special option IMHO. > IMHO, default to KVM, fallback to TCG is the most friendly default > behaviour. Except if a user expects good network performance and can't understand why they're getting 100kb/s. Regards, Anthony Liguori > > Daniel > --=20 > |: http://berrange.com -o- http://www.flickr.com/photos/dberr= ange/ :| > |: http://libvirt.org -o- http://virt-manage= r.org :| > |: http://autobuild.org -o- http://search.cpan.org/~dan= berr/ :| > |: http://entangle-photo.org -o- http://live.gnome.org/gt= k-vnc :| From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:33317) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TIlHd-0002Tp-7r for qemu-devel@nongnu.org; Mon, 01 Oct 2012 15:04:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TIlHb-0002OC-HI for qemu-devel@nongnu.org; Mon, 01 Oct 2012 15:04:01 -0400 Received: from mail-ob0-f173.google.com ([209.85.214.173]:40500) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TIlHb-0002Nz-Bw for qemu-devel@nongnu.org; Mon, 01 Oct 2012 15:03:59 -0400 Received: by obbwc18 with SMTP id wc18so3110446obb.4 for ; Mon, 01 Oct 2012 12:03:58 -0700 (PDT) From: Anthony Liguori In-Reply-To: <20121001164730.GC15554@redhat.com> References: <20120930191146.GA20012@amt.cnet> <50694EC1.8060006@siemens.com> <20121001093102.GA14797@amt.cnet> <50696E9E.7030302@siemens.com> <87zk468h3y.fsf@codemonkey.ws> <50699CDC.1010604@redhat.com> <87wqzap9ui.fsf@codemonkey.ws> <5069A9DF.4040606@siemens.com> <5069C814.7010201@suse.de> <20121001164730.GC15554@redhat.com> Date: Mon, 01 Oct 2012 14:03:54 -0500 Message-ID: <87626u9fqd.fsf@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH] kvm: Set default accelerator to "kvm" if the host supports it List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" , Andreas =?utf-8?Q?F=C3=A4r?= =?utf-8?Q?ber?= Cc: kvm , Scott Moser , Jan Kiszka , Marcelo Tosatti , Michael Tokarev , qemu-devel , Bruce Rogers , Avi Kivity , Cole Robinson , Paolo Bonzini "Daniel P. Berrange" writes: > On Mon, Oct 01, 2012 at 06:43:00PM +0200, Andreas F=C3=A4rber wrote: >> Hello Jan, >>=20 >> Am 01.10.2012 16:34, schrieb Jan Kiszka: >> > If we built a target for a host that supports KVM in principle, set the >> > default accelerator to KVM as well. This also means the start of QEMU >> > will fail to start if KVM support turns out to be unavailable at >> > runtime. >>=20 >> From a distro point of view this of course means that we will build >> against KVM and that the new KVM default will start to fail for users on >> very old hardware. Can't we do a runtime check to select the default? > > NB, this is *not* only about old hardware. There are plenty of users who > use QEMU inside VMs. One very common usage I know of is image building > tools which are run inside Amazon VMs, using libguestfs & QEMU. But libguest can set it's accelerator option to whatever it wants. If your running QEMU under a VM, it's pretty reasonable to have to use a special option IMHO. > IMHO, default to KVM, fallback to TCG is the most friendly default > behaviour. Except if a user expects good network performance and can't understand why they're getting 100kb/s. Regards, Anthony Liguori > > Daniel > --=20 > |: http://berrange.com -o- http://www.flickr.com/photos/dberrange= / :| > |: http://libvirt.org -o- http://virt-manager.or= g :| > |: http://autobuild.org -o- http://search.cpan.org/~danberr= / :| > |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vn= c :|