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

[Thomas Huth]

On 07/01/2020 13.54, Daniel P. Berrangé wrote:
> On Tue, Jan 07, 2020 at 01:23:18PM +0100, Paolo Bonzini wrote:
>> On 07/01/20 13:18, Thomas Huth wrote:
>>> I don't think we need a separate priority parameter here. But IMHO it's
>>>  really rather common practice to prioritize the last option. So while
>>> it might be more "self-explanatory" to a CLI newbie if the first
>>> occurrence got the highest priority, it might be rather confusing
>>> instead for a CLI veteran...?
>>
>> Prioritising the last certainly makes sense for a choose-one-only
>> option, but I'm not sure it's the same for a choose-best option.  After
>> all it was -machine accel=kvm:tcg, not -machine accel=tcg:kvm...
> 
> IIUC, the main use case for specifying multiple accelerators is
> so that lazy invokations can ask for a hardware virt, but then get
> fallback to TCG if not available. For things that should be platform
> portabile, there's more than just kvm to consider though, as we have
> many accelerators.  Listing all possible accelerators is kind of
> crazy though no matter what the syntax is.
> 
> How about taking a completely different approach, inspired by the
> -cpu arg and implement:
> 
>     -machine accel=best

Something like that sounds like the best solution to me, but I'd maybe
rather not call it "best", since the definition of "best" might depend
on your use-case (e.g. do you want to use a CPU close to the host or
something different which might be better emulated by TCG?).

What about "-accel any" or "-accel fastest" or something similar?

 Thomas