Re: [Qemu-devel] [PATCH] kvm: Set default accelerator to "kvm" if the host supports it

[Michael Tokarev]

On 02.10.2012 11:46, Markus Armbruster wrote:
> "Daniel P. Berrange" <address@hidden> writes:

>> IMHO, default to KVM, fallback to TCG is the most friendly default
>> behaviour.
> 
> Friendly perhaps, generating an infinite series of questions "why is my
> guest slow as molasses?" certainly.

With a warning about "switching to slow emulation mode because .."
printed at startup that becomes a non-issue, because there's no
reason to ask more questions about why it is slow - it already
said why.  Yes some may try to ask what to do, which is different.

Every howto nowadays mentions kvm modules and /dev/kvm device
permissions.

> And for each instance of the question, there's an unknown number of
> users who give QEMU a quick try, screw up KVM unknowingly, observe the
> glacial speed, and conclude it's crap.

This is, again, I think, unfair.  With the warning message it becomes
more or less obvious.

If you're talking about users who run it with -daemonize argument -
this is a) stupid to do when TRYING it out, so it's not a big deal
to lose another stupid user, and b) qemu should init everything
first and throw all warnings and fatal errors before daemonizing,
if this is not the case it should be fixed in the code.

And if you're talking about management software (libvirt and others),
it controls all the required privileges already and explicitly
requests acceleration and other stuff.

So the best thing to do is what Daniel, Aurelien, Paolo and others
are suggested: accel=kvm:tcg with a warning.

Thanks,

/mjt