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zebra: separate nht notifications from dplane_result thread
There is a CPU issue in ZEBRA when BGP installs and removes a lot of routes at the same time. The vtysh and shell become unreachable. This is the case of BGP failover scenarios with two peers, and one of the peers becoming unreachable. For each route change, it appears that nexthop tracking is called to check impact about a new route (un)availability. Two observations are done: - In the case of a specific route change, if a bigger route (or a default route is present like it is in the setup) exists, then nexthop tracking is called. there is no need to call nexthop tracking for the same default prefix, knowing that the dplane_result thread handled bulks of routes at the same time. - The first picture from the below link indicates nexthop tracking consumes time, and maintaining this activity in the zebra main thread will still result in STARVATION messages. Propose to separate the nht notifications from the dplane_result thread by creating a queue list that will store the prefixes to evaluate against nexthop tracking. Before enqueuing it, a check is done if the same prefix has not been called before. The processing is done in a separate 'rib_process_nht_thread_loop' function call. Link: FRRouting#16028 Signed-off-by: Philippe Guibert <[email protected]>
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