Re: Priority of -accel (was: [PATCH] tests/qemu-iotests: Update tests to recent desugarized -accel option)

[Paolo Bonzini <pbonzini@redhat.com>]

On 07/01/20 14:55, Christophe de Dinechin wrote:
> So what about ranking the accelerators, so that all combinaisons
> -accel=kvm:tcg, -accel=tcg:kvm, -accel kvm -accel tcg, etc would

(I assume you mean "-machine accel=kvm:tcg" and "-machine accel=tcg:kvm"
for the first two.  This is the "older" way which has now become sugar
for "-accel kvm -accel tcg").

> all pickup kvm if available, and tcg as a fallback? Implementation-wise,
> it would simply mean ranking the accelerators and updating the accelerator
> only if it’s available and better.

This is an interesting idea.  I like this better than "-accel best",
because "-accel best" has the problem that you can't add suboptions to
it (the suboptions for the various accelerators are disjoint).

It would break backwards compatibility for "-machine accel=tcg:kvm",
which so far meant "use TCG if compiled in, otherwise use KVM".  This is
not something I would have a problem with... except that "tcg:kvm" is
the default if no -accel option is provided!

Paolo