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

Øyvind Heggstad mrelendig at har-ikkje.net
Wed Mar 2 11:45:31 EST 2011

On Thu, 24 Feb 2011 11:43:33 -0600
C Anthony Risinger <anthony at extof.me> wrote:

> On Thu, Feb 24, 2011 at 11:23 AM, Jelle van der Waa <jelle at vdwaa.nl>
> wrote:
> > On Thu, 2011-02-24 at 11:07 -0600, C Anthony Risinger wrote:
> >> 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?
> qemu-kvm is always fast.  qemu is never fast -- libvirt uses
> `-enable-kvm` when i tell it to, ie. for either package.  i've tried
> recompiling the regular `qemu` package with explicit KVM support, and
> the speed is still absolutely abysmal.
> >> 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.
> >
> > Another tip for kvm usage is installing your OS on virtio [1]
> already do :-) i use all the virtio drivers -- when i say perf is bad
> i mean it's like KVM isnt even working.  i haven't `lsof` yet to make
> sure qemu (not qemu-kvm!!) is actually opening the /dev/kvm device.
> i read thru the packages of both.  i tried symlinking
> `/usr/bin/qemu-kvm -> qemu-system-x86_64` (this is what qemu-kvm
> package does) ... no difference.
> so my real question is, is anyone using the upstream package `qemu`,
> with KVM, and getting proper results?  are good results expected?
> what am i missing here.
> C Anthony
This is quite strange, I use qemu-system-x86_64 --enable-kvm regulary,
and I get near native speed in the vm. 
[oh at Alice][~]% pacman -Q qemu
qemu 0.14.0-1

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