UDP aggregation on s390x is disabled. This was done, because changing the interface feature did not work in the past (https://issues.redhat.com/browse/OCPBUGS-2532).

We have implemented a change in openshift/ovn-kubernetes (https://issues.redhat.com/browse/OCPBUGS-18935) that makes the used Go library safchain/ethtool able to change the interface features on s390x, so enabling UDP aggregation should now be possible for s390x nodes. Our proposed change is: https://github.com/openshift/cluster-network-operator/pull/2331 - this fix still needs to be verified end-to-end with a payload that includes all fixes.

Always, it is disabled in code:
https://github.com/openshift/cluster-network-operator/blob/a5b5de5098592867f39ac513dc62024b5b076044/pkg/network/ovn_kubernetes.go#L671-L674

    1. Install OpenShift cluster on s390x with OVN-Kubernetes

Interface feature rx-udp-gro-forwarding is disabled.

Interface feature rx-udp-gro-forwarding is enabled.    

There is a config map for disabling the interface feature if needed (namespace openshift-network-operator, config map udp-aggregation-config, value disable-udp-aggregation = "true" disables UDP aggregation). This should be kept.