Re: Priority of -accel

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 1/7/20 1:18 PM, Thomas Huth wrote:
> On 07/01/2020 11.14, Paolo Bonzini wrote:
>> On 07/01/20 11:03, Thomas Huth wrote:
>>>>   
>>>>   vm = QEMUMachine(iotests.qemu_prog)
>>>> -vm.add_args('-machine', 'accel=kvm:tcg')
>>>> +vm.add_args('-accel', 'kvm', '-accel', 'tcg')
>>> Looking at this, I wonder whether we really want the "-accel" option to
>>> prioritize the accelerators in the order of appearance? A lot of other
>>> CLI tools give the highest priority to the last parameter instead, e.g.
>>> "gcc -O3 -O1" compiles with -O1, and not with -O3.
>>>
>>> Also I think it might be quite common that there are shell scripts which
>>> call "qemu-system-xxx -accel xyz $*" ... and if we don't invert the
>>> priorities of -accel, it will be impossible to override -accel in that
>>> case...
>>
>> Hmm, it does match "-machine accel=kvm:tcg" and in general I think it's
>> more self-explanatory.  However, it is indeed less friendly to scripts.
>>   On one hand those could be changed to place "-accel xyz" after $* (or
>> better "$@"), on the other hand we could also add a priority option to
>> "-accel".  What do you think?
> 
> 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...?
> 
> What do others on the list here think about this?

We can make CLI more complex by adding a 'priority' option:

   -accel tcg,priority=1 -accel kvm,priority=0