Re: [Xen-users] kqemu kernel module

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Is useful to accelerate xen guest or not?

It's not possible to use kqemu to accelerate an HVM guest.  HVM mode provides 
(I believe) a more complete virtual environment than kqemu does if you have 
the available hardware support (I've not seen a direct performance comparison 
though).  If you don't have hardware support for virtualisation it's not 
possible to use kqemu instead because it won't co-exist with Xen.

It's not possible to run kqemu within a paravirt Xen guest because it requires 
ring0 privileges, which they don't have.  It might work in an HVM guest but I 
wouldn't expect it to perform particularly well - also, it might conceivably 
not work as expected, since the tricks it uses for full virt might tickle 
some corner cases in the HVM code...  I've not tried this though, but nesting 
virtualisers can lead to weird results ;-)

There is the prospect of using kqemu-like techniques to provide accelerated IO 
and maybe full virt support on non-HVM guests - this is being done as part of 
the V2E project.  Some of this functionality will be rolled into future 
releases of Xen.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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