Add nb_cfg_timestamp to SB_Global for propagation latency.#306
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Add nb_cfg_timestamp to SB_Global for propagation latency.#306tehhobbit wants to merge 1 commit into
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Large scale OVN deployments commonly disable the per-chassis nb_cfg write-back mechanism by setting options:enable_chassis_nb_cfg_update to false. With thousands of hypervisors each writing their nb_cfg completion back to Chassis_Private on every generation, the resulting write amplification can overload the southbound OVSDB cluster. Disabling write-back eliminates this pressure but also removes the only existing signal for measuring how long a northbound change takes to reach each hypervisor. OVN_Northbound already records nb_cfg_timestamp in NB_Global when ovn-northd advances nb_cfg, but hypervisors connect to the southbound database only. This patch adds the same timestamp to SB_Global, written atomically with each nb_cfg update. ovn-controller reads this value and stores it in the local OVS bridge external_ids as ovn-nb-cfg-sb-ts alongside the existing ovn-nb-cfg-ts (local completion time). An external collector such as ovs_exporter can read both values from the bridge and compute per-chassis propagation latency histograms without any writes to the southbound database, keeping measurement overhead independent of fleet size. Placing the timestamp in SB_Global rather than requiring collectors to reach the northbound database means it travels transparently through any relay or VPN between the southbound cluster and the hypervisor, naturally including that transit in the measurement. Testing: confirmed in OVN sandbox and a two-container central/HV setup that nb_cfg_timestamp is written to SB_Global on each nb_cfg advance, propagated to br-int external_ids as ovn-nb-cfg-sb-ts, and continues to update correctly when enable_chassis_nb_cfg_update is set to false. Signed-off-by: Loke Berne <loke@tehhobbit.net> Assisted-by: Claude Sonnet 4.6 Submitted-at: ovn-org#306 Signed-off-by: Numan Siddique <numans@ovn.org> Signed-off-by: Dumitru Ceara <dceara@redhat.com>
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Large scale OVN deployments commonly disable the per-chassis nb_cfg write-back mechanism by setting options:enable_chassis_nb_cfg_update to false. With thousands of hypervisors each writing their nb_cfg completion back to Chassis_Private on every generation, the resulting write amplification can overload the southbound OVSDB cluster. Disabling write-back eliminates this pressure but also removes the only existing signal for measuring how long a northbound change takes to reach each hypervisor. OVN_Northbound already records nb_cfg_timestamp in NB_Global when ovn-northd advances nb_cfg, but hypervisors connect to the southbound database only. This patch adds the same timestamp to SB_Global, written atomically with each nb_cfg update. ovn-controller reads this value and stores it in the local OVS bridge external_ids as ovn-nb-cfg-sb-ts alongside the existing ovn-nb-cfg-ts (local completion time). An external collector such as ovs_exporter can read both values from the bridge and compute per-chassis propagation latency histograms without any writes to the southbound database, keeping measurement overhead independent of fleet size. Placing the timestamp in SB_Global rather than requiring collectors to reach the northbound database means it travels transparently through any relay or VPN between the southbound cluster and the hypervisor, naturally including that transit in the measurement. Testing: confirmed in OVN sandbox and a two-container central/HV setup that nb_cfg_timestamp is written to SB_Global on each nb_cfg advance, propagated to br-int external_ids as ovn-nb-cfg-sb-ts, and continues to update correctly when enable_chassis_nb_cfg_update is set to false. Signed-off-by: Loke Berne <loke@tehhobbit.net> Assisted-by: Claude Sonnet 4.6
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Large scale OVN deployments commonly disable per-chassis nb_cfg
write-back by setting options:enable_chassis_nb_cfg_update to
false. With thousands of hypervisors each writing completion
back to Chassis_Private on every generation, the resulting write
amplification can overload the southbound OVSDB cluster.
Disabling write-back eliminates this pressure but also removes
any signal for measuring how long a northbound change takes to
reach each hypervisor.
OVN_Northbound already records nb_cfg_timestamp in NB_Global
when ovn-northd advances nb_cfg, but hypervisors connect to the
southbound database only. This patch adds the equivalent
timestamp to SB_Global, written atomically with each nb_cfg
update. ovn-controller reads this value and stores it in the
local OVS bridge external_ids as ovn-nb-cfg-sb-ts alongside the
existing ovn-nb-cfg-ts (local completion time). An external
collector can read both values from the bridge and compute
per-chassis propagation latency histograms without any writes to
the southbound database, keeping measurement overhead independent
of fleet size.
Placing the timestamp in SB_Global rather than requiring
collectors to reach the northbound database means it travels
transparently through any relay or VPN between the southbound
cluster and the hypervisor, naturally including that transit in
the measurement.
Tested in the OVN sandbox and a two-container central/HV setup.
Confirmed nb_cfg_timestamp is written to SB_Global on each
nb_cfg advance, propagated to br-int external_ids as
ovn-nb-cfg-sb-ts, and continues updating correctly when
enable_chassis_nb_cfg_update is false.
Assisted-by: Claude Sonnet 4.5, Claude Code