Re: [Qemu-devel] [PATCH] accel: Improve selection of the default accelerator

[Thomas Huth]

On 2018-10-09 15:14, Markus Armbruster wrote:
> Markus Armbruster <address@hidden> writes:
> 
>> Peter Maydell <address@hidden> writes:
>>
>>> On 5 October 2018 at 15:13, Thomas Huth <address@hidden> wrote:
>>>> When compiling with "--disable-tcg", we currently still use "tcg"
>>>> as default accelerator. "kvm" should be used in this case instead.
>>>
>>> This part is non-controversial and makes good sense.
>>
>> Agreed.
>>
>>>> Also, some downstream distros provide QEMU binaries which have "kvm"
>>>> in their names (e.g. "qemu-kvm" on RHEL or "kvm" on Ubuntu) that use
>>>> KVM by default - and some users might want to do something similar
>>>> with upstream binaries, too. Accomodate them by using "kvm:tcg" as
>>>> default when we detect such a binary name.
>>>
>>> This part is much riskier and less clearly a good plan --
>>> do we really want our behaviour to vary based on the name
>>> of the executable? Distros who want that sort of qemu-kvm
>>> wrapper generally are providing it already (the Ubuntu one
>>> is a 2-line shell script).
>>
>> I hate it when argv[0] affects behavior[*].  I hate shell wrappers less.
>>
>> If a system provides just one qemu executable, and its default
>> accelerator should be something other than tcg:kvm, then there's a use
> 
> Correction: "other than tcg".  See configure_accelerator().
> 
> Remind me, why is "tcg" a good default?

"It's been always like this and we're keen on backward compatibility" ?

 Thomas