KVM Q35 Virtual Machines , SR-IOV PCI-E Bridges and OpenBSD jitter on attached network

Hello,
Has anyone seen jitter from 0.5ms to 500ms
on PCI-E attached (SR-IOV) Physical function / virtual function
Network interfaces on OpenBSD Machines running on
a KVM Virtual machine type (Q35) ?

any tips for diagnosing what is causing the jitter ?
I have ruled out the driver Ixl by comparing physical / bare metal
performance vs
performance when the physical function of the nic is passed through
to the KVM Q35 guest

I have also ruled out the hypervisor as centos Guest VMs running with
the same hardware don't suffer from the jitter issue



--
Kindest regards,
Tom Smyth.