Frequently update Chassis external_ids high cpu usage on ovn-controller process

[LI.Yujie]

commit : https://github.com/openstack/networking-ovn/commit/7cf92ee960697d284f58ab9c26dab607b3685f57

    def agent_alive(self, chassis, type_):
        nb_cfg = chassis.nb_cfg
        id_ = chassis.uuid
        key = ovn_const.OVN_LIVENESS_CHECK_EXT_ID_KEY
        if type_ == ovn_const.OVN_METADATA_AGENT:
            id_ = utils.ovn_metadata_name(chassis.uuid)
            nb_cfg = int(chassis.external_ids.get(
                ovn_const.OVN_AGENT_METADATA_SB_CFG_KEY, 0))
            key = ovn_const.METADATA_LIVENESS_CHECK_EXT_ID_KEY

        try:
            updated_at = timeutils.parse_isotime(chassis.external_ids[key])
        except KeyError:
            updated_at = timeutils.utcnow(with_timezone=True)

        if self._nb_ovn.nb_global.nb_cfg == nb_cfg:
            # update the time of our successful check
            value = timeutils.utcnow(with_timezone=True).isoformat()
            self._sb_ovn.db_set('Chassis', chassis.uuid,
                                ('external_ids', {key: value})).execute(
                check_error=True)

[root@openstack-con01 ~(keystone_admin)]# ovn-sbctl list Chassis 7cc5646c-6eb1-4998-85d0-74e9bd7f385f
_uuid : 984ad0f6-478d-4fa5-a863-5e5da9642756
encaps : [1c7ac35f-2298-4ce6-81be-775826ef5221, e28e49e9-8e98-413b-a5f1-0c58f15547bd]
external_ids : {datapath-type=system, iface-types="erspan,geneve,gre,internal,ip6erspan,ip6gre,lisp,patch,stt,system,tap,vxlan", is-interconn="false", "neutron:liveness_check_at"="2020-05-08T09:36:53.903170+00:00", ovn-bridge-mappings="", ovn-chassis-mac-mappings="", ovn-cms-options=""}
hostname : openstack-compute108
name : "7cc5646c-6eb1-4998-85d0-74e9bd7f385f"
nb_cfg : 22805
transport_zones : []
vtep_logical_switches: []
[root@openstack-con01 ~(keystone_admin)]# ovn-sbctl list Chassis 7cc5646c-6eb1-4998-85d0-74e9bd7f385f
_uuid : 984ad0f6-478d-4fa5-a863-5e5da9642756
encaps : [1c7ac35f-2298-4ce6-81be-775826ef5221, e28e49e9-8e98-413b-a5f1-0c58f15547bd]
external_ids : {datapath-type=system, iface-types="erspan,geneve,gre,internal,ip6erspan,ip6gre,lisp,patch,stt,system,tap,vxlan", is-interconn="false", "neutron:liveness_check_at"="2020-05-08T09:37:23.970521+00:00", ovn-bridge-mappings="", ovn-chassis-mac-mappings="", ovn-cms-options=""}
hostname : openstack-compute108
name : "7cc5646c-6eb1-4998-85d0-74e9bd7f385f"
nb_cfg : 22806
transport_zones : []
vtep_logical_switches: []

Frequently update Chassis external_id
high cpu usage on ovn-controller process