On Tue, Jun 26, 2018 at 03:05:33PM +0200, Paolo Bonzini wrote: > On 26/06/2018 14:29, Eduardo Habkost wrote: > > On Tue, Jun 26, 2018 at 07:57:18AM +0200, Paolo Bonzini wrote: > >> On 25/06/2018 21:51, Eduardo Habkost wrote: > >>> 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. > >> > >> It would be a guest ABI breakage for TCG guests, so it would only apply > >> to new machine types. I don't think it's worth the complication. > > > > That's exactly the point: I want to stop promising a stable guest > > ABI when the accelerator is omitted, because I see no benefit in > > wasting energy on this. > > On the other hand I see no benefit in changing a default that people are > obviously not using (since most people use KVM, not TCG). Distros will > keep shipping, and people will keep using qemu-kvm even if we change the > default.
Not changing the default is different from promising we will keep ABI compatibility if the accelerator is omitted. I just want to get rid of the latter. > > (I don't think we ever kept the guest ABI correctly with TCG, by > > the way.) > > It would not be any different from KVM. Less tested and likely to be > more buggy, yes, but not particularly harder. We can keep trying to not break it when "-accel tcg" is explicitly provided. -- Eduardo