Libvirt vs QEMU benefits

[Daniel P. Berrangé]

On Wed, Apr 06, 2022 at 12:44:37PM +0000, M, Shivakumar wrote:
> Hello,
> 
> For one of our case validation, we were using direct QEMU commands before for VM creation as it was easier to configure the VMs. Inside VM we do run the real-time latency test.
> Recently we switched to libvirt for the VM creation and deletion. Surprisingly, we do see a significant increase in the real-time latency performance for the VMs launched through the libvirt.
> 
> W.r.t configuration wise both VMs are the same, we just converted the existing QEMU commands into libvirt XMLs.

It would be useful to share your QEMU command line args seen both
with directly running QEMU and via libvirt. I'd be really suprised
if your direct config was exactly the same as libvirt's.

> I am wondering what and all the features which libvirt has,
> improving this performance.

If it isn't related to QEMU configuration, then most likely candidate
is the use of cgroups for placing VMs.

With regards,
Daniel
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