Re: Priority of -accel

[Daniel P . Berrangé]

On Tue, Jan 07, 2020 at 03:20:40PM +0100, Philippe Mathieu-Daudé wrote:
> On 1/7/20 3:14 PM, Thomas Huth wrote:
> > 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?
> 
> 'any' is a russian roulette, you don't want it to return 'qtest' ;)

We could make it return "qtest" only on April 1st ;-P

Regards,
Daniel
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