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

[Kevin Wolf]

Am 07.01.2020 um 18:43 hat Christophe de Dinechin geschrieben:
> > 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!
> 
> What is the rationale for picking tcg over kvm?
> 
> My guess is that when this was selected, KVM was the new fancy unstable
> thing and this was deemed the safe choice. My other guess is that this was
> around 1907 or so :-) My third guess is that you will probably provide me
> with a much better rationale ;-)

I know I intentionally disabled KVM in the past for debugging guests
because TCG allowed a few more things there (most of -d doesn't do
anything with KVM, and I think the gdb stub also had some restrictions).

Requiring an explicit '-accel tcg' for such cases might be reasonable
enough, though.

(And if we make this change and therefore break with the habit that
Peter mentioned - leaving defaults unchanged - could we make more
changes that better reflect a typical use case today? For example, I
doubt most people can do with only 128 MB of RAM in the guest.)

Kevin