Conflicting parameters on qemu call

[Jan Walzer]

On 21. Aug 2020, at 11:20, Daniel P. Berrangé <berrange at redhat.com> wrote:
> On Fri, Aug 21, 2020 at 11:19:14AM +0200, Jan Walzer wrote:
>> Hi Daniel,
>>> On 21. Aug 2020, at 11:07, Daniel P. Berrangé <berrange at redhat.com> wrote:
>>> On Fri, Aug 21, 2020 at 11:00:27AM +0200, Jan Walzer wrote:
>>>> On 21. Aug 2020, at 10:38, Daniel P. Berrangé <berrange at redhat.com> wrote:
>>>>> On Thu, Aug 20, 2020 at 08:11:30PM +0200, Jan Walzer wrote:
>>>>>> Hi Lists,
>>>>>> 
>>>>>> I currently have the issue of wanting to use emu-system-x86_64 on a ppc64le platform.
>>>>>> 
>>>>>> It is imperative to pass the "-accel tcg,thread=multi” parameter to qemu 
>>>>>> when starting an instance, as without that, it will only use one thread 
>>>>>> and hence of limited/no use.
>>>>>> 
>>>>>> The problem is, that libvirt itself, passes “-machine q35,accel=tcg” to
>>>>>> qemu, which is a different parameter, that conflicts with the other one.
>>>>>> 
>>>>>> Can we discuss, if I either have overlooked something, or is there a workaround, or is this a bug?
>>>>> 
>>>>> What you're trying todo is intentionally not available.
>>>>> 
>>>>> The memory ordering constraints needed for running x86_64 guests on ppc64
>>>>> hosts cannot be satisfied, so multi-threaded TCG is not available.
>>>>> 
>>>>> For any guest/host combination where multi-thread TCG is safe to use, QEMU
>>>>> will enable it automatically, so nothing is required in libvirt.
>>>> 
>>>> 
>>>> Hi Daniel,
>>>> Thanks for the answer. I’ve read (and understand) the warnings and their implications.
>>>> 
>>>> So there’s not even an “I know what I’m Doing”-Switch?
>>> 
>>> […]
>>> <qemu:commandline>
>>>   <qemu:arg value='-accel'/>
>>>   <qemu:arg value='tcg,thread=multi'/>
>>> </qemu:commandline>
>> 
>> As I wrote: This is what I’m already doing
>> The Problem is that this conflicts with, libvirt already using the parameter: “-machine ..,accel=tcg”
>> And I can’t get libvirt, to stop passing this parameter.
> 
> It shouldn't matter.  QEMU should aggregate the settings from the
> multiple args, with latter args overriding earlier args if there is
> any duplication..


That was what I thought to, but:

# qemu-system-x86_64  -machine q35,accel=tcg -accel tcg,thread=multi --smp 8 -m 8
Unable to init server: Could not connect: Connection refused
qemu-system-x86_64: The -accel and "-machine accel=" options are incompatible

# qemu-system-x86_64 --version
QEMU emulator version 5.0.0 (Debian 1:5.0-14)
Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers

I’m already discussing that on qemu list:
https://lists.nongnu.org/archive/html/qemu-ppc/2020-08/msg00338.html <https://lists.nongnu.org/archive/html/qemu-ppc/2020-08/msg00338.html>

But I’d like to track that issue in multiple directions.

Greetings, Jan

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