From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35362) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fWTWE-0007gD-Dr for qemu-devel@nongnu.org; Fri, 22 Jun 2018 17:23:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fWTW6-0007SJ-0S for qemu-devel@nongnu.org; Fri, 22 Jun 2018 17:22:58 -0400 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> <20180622193522.GI7451@localhost.localdomain> From: Paolo Bonzini Message-ID: <743d495e-51cd-8c8e-293e-026b8dece74a@redhat.com> Date: Fri, 22 Jun 2018 23:22:43 +0200 MIME-Version: 1.0 In-Reply-To: <20180622193522.GI7451@localhost.localdomain> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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: Eduardo Habkost , Thomas Huth Cc: Cornelia Huck , Markus Armbruster , "=?UTF-8?Q?Daniel_P._Berrang=c3=a9?=" , zhang.zhanghailiang@huawei.com, Ben Warren , qemu-trivial@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi On 22/06/2018 21:35, Eduardo Habkost wrote: >>> 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. >=20 > 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. We can, we don't necessarily want it. The status quo is that people using KVM are invoking qemu as qemu-kvm, people using TCG are invoking qemu as qemu-system-*. All distros are shipping a qemu-kvm or more rarely kvm binary, which is invariably a wrapper script except for RHEL because RHEL doesn't have a qemu-system-* binary at all. By the way, changing qemu-system-*'s default to e.g. RHEL's "kvm or tcg" would not help distros that have "-accel kvm" in their /usr/bin/qemu-kvm script. All in all, it seems simpler for me to take the status quo, which is what non-RHEL distros do, and make it part of upstream. Paolo