[arch-general] qemu-kvm vs. qemu upstream

[Jelle van der Waa]

On Thu, 2011-02-24 at 11:07 -0600, C Anthony Risinger wrote: 
> On Thu, Feb 24, 2011 at 10:53 AM, Jelle van der Waa <jelle at vdwaa.nl> wrote:
> > On Thu, 2011-02-24 at 10:33 -0600, C Anthony Risinger wrote:
> >> On Wed, Feb 23, 2011 at 7:38 PM, Allan McRae <allan at archlinux.org> wrote:
> >> >
> >> > If this is virtualbox specific, I'd try qemu-kvm.
> >>
> >> hey,
> >>
> >> i was just trying to get a concrete answer about this the other day,
> >> so maybe you can clarify because i keep reading conflicting and/or
> >> outdated information.
> >>
> >> AFAICS, qemu-kvm is still _different_ from upstream kvm support in
> >> qemu, correct?  i tried rebuilding qemu several times, ensuring i had
> >> all the options i wanted (SPICE/kvm/etc) and i was getting absolutely
> >> <expletive deleted> performance -- switch to qemu-kvm and she's
> >> blazing again, yet many places seem to suggest they are one and the
> >> same.
> >>
> >> i see they definitely have different sources, but would you/anyone
> >> care to elaborate on the relationship?
> >
> > IIRC
> >
> > qemu-kvm is  the QEMU + KVM provided by the kvm project and normal QEMU
> > can use KVM as virtualizer. (correct me if i am wrong )
> >
> > from wikipedia:
> >        By itself, KVM does not perform any emulation. Instead, a
> >        user-space program uses the /dev/kvm interface to set up the
> >        guest VM's address space, feeds it simulated I/O and maps its
> >        video display back onto the host's. At least two programs
> >        exploit this feature: a modified version of Qemu, and Qemu
> >        itself since version 0.10.0.
> >
> > In short, if you have VT extensions, use qemu-kvm, if not use qemu since
> > it emulates ( costs much cpu though ).
> >
> > QEMU/KVM is for me the best way to run windows, KVM is in the kernel so
> > now rebuilding of modules, completely open source and it has nice
> > features.
> 
> hmm, soo qemu doesn't actually use the VT extensions?  wtf is the
> point then? 
QEMU is an emulator -> so for ARM for example 
> this is what i don't understand; if qemu supports KVM via
> the `-enable-kvm` switch why does it suck so much -- it seems just as
> slow to me as no KVM support at all. 
Here it's not, are you using qemu-kvm or some selfcompiled version? 
> I have a server that runs
> several KVM/libvirt instances (windows being one of them purely for
> ... i dont even know) so i'm pretty familiar with it all, but i'm just
> trying to get solid info why there is such a huge performance gap when
> the both "use KVM".  i thought KVM itself did all the VT handling.
> 
> C Anthony

Another tip for kvm usage is installing your OS on virtio [1] 


[1] http://www.linux-kvm.org/page/Using_VirtIO_NIC

-- 
Jelle van der Waa
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