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Date: Wed, 6 Sep 2017 17:54:13 +0200
From: Cornelia Huck <cohuck@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH RFC] accel: default to an actually
 available accelerator
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Laurent Vivier <lvivier@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Thomas Huth <thuth@redhat.com>, Kevin Wolf <kwolf@redhat.com>, Max Reitz <mreitz@redhat.com>

On Wed, 6 Sep 2017 15:35:16 +0100
Peter Maydell <peter.maydell@linaro.org> wrote:

> On 6 September 2017 at 12:29, Cornelia Huck <cohuck@redhat.com> wrote:
> > On Wed,  6 Sep 2017 11:49:27 +0200
> > Cornelia Huck <cohuck@redhat.com> wrote:  
> >> @@ -79,8 +98,7 @@ void configure_accelerator(MachineState *ms)
> >>
> >>      accel = qemu_opt_get(qemu_get_machine_opts(), "accel");
> >>      if (accel == NULL) {
> >> -        /* Use the default "accelerator", tcg */
> >> -        accel = "tcg";
> >> +        accel = default_accelerator();  
> >
> > It actually may be easier to just switch the default to
> > "tcg:kvm:xen:hax". Haven't tested that, though.  
> 
> Does it make sense to include Xen in the default list?
> I don't know much about Xen but I was under the impression
> that it's a special purpose thing that you can only use
> as part of a Xen setup, whereas tcg, kvm, hax are all
> more-or-less interchangeable ways to run a VM under a
> Linux/etc host. Do I have the wrong end of the Xen stick?

I'm unfortunately not familiar with xen either.

I was going with what configure considers as an available accelerator
(in supported_target()). FWIW, I can build x86_64 with xen as the only
available accelerator, but have not been able to get it to work (in all
of the 5 minutes I tried). I can't get it to build with hax as the only
accelerator (although configure does not complain; I might be missing
something).

Switching the default from "tcg" to "tcg:kvm" would already fix the
problem for s390x ;), but maybe someone else has a better idea?