Re: [PATCH v2] qemu-kvm: Switch to upstream -enable-kvm semantics

[Avi Kivity <avi@redhat.com>]

On 12/22/2010 02:33 PM, Markus Armbruster wrote:
> We currently enable KVM by default, and when it's not available, we
> print a message and fall back to TCG.  Option -enable-kvm is ignored.
> Option -no-kvm suppresses KVM.
>
> Upstream works differently: KVM is off by default, -enable-kvm
> switches it on.  -enable-kvm terminates the process unsuccessfully if
> KVM is not available.
>
> upstream qemu   |  default  |-enable-kvm
> ----------------+-----------+-----------
> KVM available   | disabled  |  enabled
> KVM unavailable | disabled  |    fail
>
> qemu-kvm        |  default  |-enable-kvm|  -no-kvm
> ----------------+-----------+-----------+----------
> KVM available   |  enabled* |  enabled  |  disabled
> KVM unavailable | disabled  | disabled* |  disabled
>
> * differs from upstream
>
> Users of qemu and qemu-kvm need to be aware of these differences to
> enable / disable use of KVM reliably.  This is bothersome.
>
> Consider -enable-kvm when KVM is unavailable: If the user expects
> qemu-kvm behavior (fall back), but qemu fails, he'll likely be
> surprised and unhappy.  If the user expects upstream behavior (fail),
> but qemu-kvm falls back to TCG, the guest runs slow as molasses, and
> the user will likely be confused and unhappy (unless he spots and
> understands the "disable KVM" message).
>
> Eventually, we'll sort this upstream with -accel (defaults tied to
> machine type).  Until then, this patch reduces the difference to
> upstream so that most users shouldn't need to be aware of them.
>
> Make -enable-kvm behave just like in upstream: enable KVM, fail if not
> available.  But retain current default behavior: enable KVM, fall back
> to TCG.
>
> qemu-kvm new    |  default  |-enable-kvm|  -no-kvm
> ----------------+-----------+-----------+-----------
> KVM available   |  enabled* |  enabled  |  disabled
> KVM unavailable | disabled  |    fail+  |  disabled
>
> * differs from upstream
> + changed by this patch
>
> Bonus fix: -no-kvm -enable-kvm now enables KVM.  Before, it disabled it.
>

Applied, thanks.

-- 
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