On 01/02/2011 03:18 AM, Avi Kivity wrote:
On 01/02/2011 12:15 PM, Jan Kiszka wrote:
Does any qemu-kvm user rely on the automatic fallback to TCG if KVM
initialization fails?
We don't know...
Speaking as an actual user of the behaviour - I wouldn't say I became
reliant on it when I had distro kernel updates that stopped my
hand-built kvm modules from loading and I didn't notice, but in truth I
was taking advantage of it on powerful enough hardware 4x3GHz/8GB. On my
2x2.3GHz/3GB laptop it was easier just to boot my 1x600MHz/2GB laptop
with a copy of XP rather than try a Win7 or XP VM without kvm.
If not, then just set kvm_allowed to 1 in qemu-kvm
and leave the rest as upstream provides it. This fallback is really
annoying, specifically as the only point of qemu-kvm is, well, running
over KVM.
I agree, upstream's behaviour is better, and the proposed -accel is even
better. But we can't just change behaviour randomly, even if it's an
improvement.
If the behaviour was as described by Jan I would have been forced to put
the effort into re-building kvm modules against my updated kernel sooner
or intentionally adjust my qemu command line to disable kvm. You also
make a good point but I would say in response that I was encouraged to
tolerate a reduction in utility by the current behaviour rather than
deal with what's really my own configuration error on my hosts and I
think then it's an improvement for qemu-kvm with kvm_allowed != 0 to
fail to load when kvm is not present. Your point comes down to the guy
with "hosted services" on VMs that he guarantees to always be running
(and is dependent on the current behaviour for it). He will think
differently from me and be especially mad if he doesn't read the
release-notes when he updates but it's not like he couldn't adjust the
scripts he already starts qemu-kvm with to check for the error and retry
with -no-kvm if appropriate...presumably upstream has an equally usable
though non-specific error code to what happens in Markus's patch.
--
David.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
