libvirt users - Aug 2020 - Re: Libvirt qemu-system-x86_64 on ppc64le no multi threading

On Mon, Aug 03, 2020 at 01:45:45PM +0000, Kim-Norman Sahm
wrote:
> hi,
> 
> i’m running Debian 10 on POWER9 and would like to spawn x86_64 emulated
VMs.
> The virtual machine is configured to run with 8 vpus but it’s very slow.
> On the host you can see that the qemu-system-x86_64 process is using just
one core!
> 
> Ppc64le guests are using multi cores, so its looks like an config problem
or software bug with the x86 emulator.
snip
> Does anybody knows this problem?
You've not mentioned what QMEU version or what libvirt version you have.

Historically though emulation was single threaded. Only with MTTCG has
it become multi-threaded and thus able to use all cores for vCPUs. THat
is a few years old now though, so most distros should have MTTCG in some
form or another if reasonably up2date.

Regards,
Daniel
-- 
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On Mon, Aug 03, 2020 at 03:35:49PM +0100, Daniel P. Berrangé
wrote:
> On Mon, Aug 03, 2020 at 01:45:45PM +0000, Kim-Norman Sahm wrote:
> > hi,
> > 
> > i’m running Debian 10 on POWER9 and would like to spawn x86_64
emulated VMs.
> > The virtual machine is configured to run with 8 vpus but it’s very
slow.
> > On the host you can see that the qemu-system-x86_64 process is using
just one core!
> > 
> > Ppc64le guests are using multi cores, so its looks like an config
problem or software bug with the x86 emulator.
> 
> snip
> 
> > Does anybody knows this problem?
> 
> You've not mentioned what QMEU version or what libvirt version you
have.
Actually this doens't matter.
> 
> Historically though emulation was single threaded. Only with MTTCG has
> it become multi-threaded and thus able to use all cores for vCPUs. THat
> is a few years old now though, so most distros should have MTTCG in some
> form or another if reasonably up2date.
x86_64 guest on ppc64 host simply cannot use MTTCG at all, so will always
be restricted to 1 thread. If you want concurrency you'll need to run on
a real x86_64 host.

Regards,
Daniel
--
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|