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Re: Priority of -accel

From: Philippe Mathieu-Daudé
Subject: Re: Priority of -accel
Date: Tue, 7 Jan 2020 13:34:23 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2

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

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

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