From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45235) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fWRqF-0003qw-Tt for qemu-devel@nongnu.org; Fri, 22 Jun 2018 15:35:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fWRqC-00074w-Jc for qemu-devel@nongnu.org; Fri, 22 Jun 2018 15:35:31 -0400 Date: Fri, 22 Jun 2018 16:35:22 -0300 From: Eduardo Habkost Message-ID: <20180622193522.GI7451@localhost.localdomain> References: <1528866321-23886-5-git-send-email-thuth@redhat.com> <20180613133840.GK24528@stefanha-x1.localdomain> <20180613134452.GU19901@redhat.com> <20180613151942.GC19901@redhat.com> <87k1r24quk.fsf@dusky.pond.sub.org> <20180619171539.0adc90d6.cohuck@redhat.com> <20180622181108.GY7451@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [RFC PATCH 4/4] qemu-options: Do not show -enable-kvm and -enable-hax in the docs anymore List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Thomas Huth Cc: Paolo Bonzini , Cornelia Huck , Markus Armbruster , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , zhang.zhanghailiang@huawei.com, Ben Warren , qemu-trivial@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi On Fri, Jun 22, 2018 at 09:19:56PM +0200, Thomas Huth wrote: > On 22.06.2018 20:11, Eduardo Habkost wrote: > > On Tue, Jun 19, 2018 at 06:16:33PM +0200, Paolo Bonzini wrote: > >> On 19/06/2018 17:15, Cornelia Huck wrote: > >>>> Why does a user have to know how to enable KVM? Oh, because our default > >>>> is "run this guest much slower than necessary". Great! > >>> Should we try again to default to a better accelerator, if possible? I > >>> don't quite recall why we didn't do so the last time that came up... > >>> was it tests? > >> > >> My plan was to create qemu-{kvm,hax,hvf,whpx} binaries that default to a > >> better accelerator, and leave qemu-system-* as defaulting to TCG. This > >> matches what distributions already do. > > > > Why is this better than using KVM by default if it's available? > > The answer is (as almost always): Compatibility with migration. Nobody > dares to sacrifice that chicken :-( We can now kill it if we announce the feature as deprecated a couple of releases in advance. If we declare that compatibility when the accelerator is omitted is deprecated in 3.0, in QEMU 3.3 we will be free to choose a different default accelerator. -- Eduardo