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X-Received-From: 2607:f8b0:4864:20::335 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Thomas Huth , Daniel Berrange , Qemu-block , QEMU Developers , Wainer dos Santos Moschetta , Max Reitz , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu=2DDaud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 7 Jan 2020 at 17:44, Christophe de Dinechin wrote: > > On 7 Jan 2020, at 15:37, Paolo Bonzini wrote: > > It would break backwards compatibility for "-machine accel=tcg:kvm", > > which so far meant "use TCG if compiled in, otherwise use KVM". This is > > not something I would have a problem with... except that "tcg:kvm" is > > the default if no -accel option is provided! > > What is the rationale for picking tcg over kvm? Command line compatibility. QEMU existed before KVM support was ever merged into it, and so the default has always been "emulate the CPU". Defaulting to KVM would be a change of behaviour for existing working command lines. The reason for using "tcg:kvm" rather than just "tcg" may be that this way a --disable-tcg QEMU does something useful, but that's just a guess. QEMU tends to prioritize "don't change behaviour for users" to a degree that is arguably counterproductive. But it's a nice easy rule to follow :-) thanks -- PMM