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. > > 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
