Cluster upgrades to 4.10 exhibits slowness and instability on s390x

Description of problem:

cluster upgrades suffer from two types of problems starting from 4.9 (4.9 to 4.10, 4.10 to 4.11):

1. cluster upgrades are observed to take a longer time (more than 75 mins)
2. cluster instability and API timeouts of primary operators are observed which fails the upgrade tests.
Kubernetes API timeout
OpenShift API timeout
OAuth API timeout
Console becomes unavailable
Image-registry becomes unavailable

Version-Release number of selected component (if applicable):
4.10

How reproducible:
upgrading an existing ocp cluster to recent 4.10 version

Steps to Reproduce:
-

Actual results:
API timeouts and cluster upgrade takes long time during upgrade.
cluster becomes unstable during upgrade.

Expected results:
cluster upgrade should be smooth within the stipulated time.

Additional info:
observed in CI environment initially.
https://prow.ci.openshift.org/view/gs/origin-ci-test/logs/periodic-ci-openshift-multiarch-master-nightly-4.10-upgrade-from-nightly-4.9-ocp-remote-libvirt-s390x/1488588046591856640