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

[Thomas Huth <thuth@redhat.com>]

On 2018-10-05 23:12, Paolo Bonzini wrote:
> On 05/10/2018 16:22, Peter Maydell wrote:
>> On 5 October 2018 at 15:13, Thomas Huth <thuth@redhat.com> 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.
> 
> Though it probably should be extended to "whpx" and "hvf" (probably
> "xen" too if !CONFIG_KVM).

Sure, I was just unsure whether anybody has ever tried to compile with
--disable-tcg and --disable-kvm and use one of those accelerators
instead? Does it work?

>>> 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 think it makes sense.  At least RHEL has qemu-kvm but no
> qemu-system-x86_64, so it has a non-upstream patch to change the
> accelerator; for other distros there are two benefits:
> 
> 1) now: they could switch to a symlink

Right, I think it's a good idea to avoid wrapper scripts - there is less
chance to get things wrong in this case.

 Thomas