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Date: Mon, 25 Jun 2018 16:51:26 -0300
From: Eduardo Habkost <ehabkost@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH 4/4] qemu-options: Do not show
 -enable-kvm and -enable-hax in the docs anymore
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>, Thomas Huth <thuth@redhat.com>, zhang.zhanghailiang@huawei.com, Ben Warren <ben@skyportsystems.com>, qemu-trivial@nongnu.org, Cornelia Huck <cohuck@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Mon, Jun 25, 2018 at 08:26:28PM +0200, Paolo Bonzini wrote:
> On 25/06/2018 19:30, Eduardo Habkost wrote:
> >>> Attentive distros could even replace the wrapper script by a link.
> >> If they are okay with replacing the "KVM only" semantics with "KVM or
> >> TCG", which I think is generally worse.
> >
> > If we can't get agreement on what's the right default for each
> > QEMU binary, I think that's yet another reason to document that
> > upstream QEMU won't guarantee ABI compatibility if -accel is
> > omitted.
> 
> Before that we should ask what the benefit is in changing the default
> for qemu-system-*.  Nobody is using it in practice to start QEMU with
> KVM enabled...

How can you be sure?  If qemu-system-* is installed with KVM
compiled in, libvirt will probe it using
"-machine none,accel=kvm:tcg" and run the VM using
"-machine $MACHINE,accel=kvm".

In either case, I'm not arguing (yet) for changing the default
upstream.  I'm just arguing for upstream QEMU to not make any
promises about the default.

-- 
Eduardo