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

[Markus Armbruster]

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?

> for making it compile-time configurable.  Reading the default from /etc/
> would also work.  Not sure such a system exists.
>
>
>
> [*] Go document the behavior with proper precision, and you might come
> to share the feeling.