Libvirt qemu-system-x86_64 on ppc64le no multi threading

[Daniel P. Berrange]

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
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