Understanding the Statistics Model in VPP for Enhanced Networking Performance

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Dive into the world of VPP with a focus on the statistics consumption model, shared memory structures, and optimistic locking techniques. Learn how to leverage these concepts for optimal network performance at FOSDEM 2022.

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Arthur de Kerhor arthurdekerhor@gmail.com Hedi Bouattour Keep appetite for the stats, it costs nothing Presentation of the statistics consumption model in VPP from the costless low-level design to their exploitation in user space FOSDEM 2022 6 February 2022 1

Vector VPP intro Packet 1 af-packet- input Packet 2 Packet 256 ethernet- input Open-source networking dataplane in user space Multi-threaded Highly optimized for performance, speed and scale Designed as a graph of nodes Supports tons of features in L2-4 such as crypto, NAT, LB, ACL, tunnels, ip4-receive ip4-input ip4-lookup ip4-drop ip4- midchain Vector host-ens5- output Packet 1 Packet 2 FOSDEM 2022 6 February 2022 2

Stats segment in VPP Shared memory Vector based Single writer, multiple readers Optimistic locking Hypothesis: number of writes << number of reads Reading the stats in shared memory costs nothing for the data plane What is costly however is to update the stats counters in the data plane: it sometimes induces some additional cacheline misses. FOSDEM 2022 6 February 2022 3

Shared memory layout Vector of stats entries Shared memory header Name: /sys/num_worker_threads Type: Scalar Data: 4 Directory vector Name: /if/tx Type: Combined counter vector Data: pointer to the vector Errors vector Epoch counter + in_progress bool Threads Name: /interfaces/eth1/tx Type: Symlink Data: - Directory index=1 - Interface index=1 Thread 1 Thread 2 Interfaces Packets: 15 Bytes: 4021 Packets: 3 Bytes: 1643 loop0 Name: /if/names Type: Name vector Data: pointer to the vector Packets: 172 Bytes: 54812 Packets: 243 Bytes: 75031 eth1 FOSDEM 2022 6 February 2022 4

Optimistic locking Take the lock = set in_progress boolean Release the lock = unset in_progress + increment epoch counter WRITE: Counter added/extended by the main thread (e.g. new interface): lock taken directory vector update (pointers may change) counters vectors updates (e.g. new row in /if/tx) lock released READ: A stats client wants to access shared memory: wait until in_progress == 0 store epoch value read the stats of interests check that (epoch == stored epoch and not in_progress) If false, retry the read No concurrency issues when adding/extending counters because it is always done under a barrier no counters updates during writes. FOSDEM 2022 6 February 2022 5

Various clients for different usages - A simple client to access raw statistics - A filesystem in user space leveraging go-fuse - A Prometheus exporter to gather statistics for applications FOSDEM 2022 6 February 2022 6

Simple client to access raw statistics Small executable Connects to the stats socket of VPP to learn about the shared memory location Allows to list and/or dump the statistics available Takes a list of regexp as input and returns the matching counters Usage: quick access to the statistics, easy to launch FOSDEM 2022 6 February 2022 7

Fuse filesystem in Golang File Node (leaf) Name Counter index Directory Node Path Epoch Root node Path = / Epoch = 1 Path = interfaces/ Epoch = 2 Epoch = 4 Path = net/ Epoch = 3 Path = sys/ Epoch = 3 OpenDir Path = eth0/ Epoch = 3 Epoch = 4 Path = eth1/ Epoch = 2 Epoch = 4 Name = last_update Counter index = 134 Name = num_threads Counter index = 21 Name = rx Counter index = 46 Name = tx Counter index = 76 Name = punt Counter index = 163 5 Open FOSDEM 2022 6 February 2022 8

Demo! FOSDEM 2022 6 February 2022 9

Calico/VPP context Calico: open-source Kubernetes networking solution and network policy Standard Linux networking pipeline mode dataplane Integrating VPP dataplane: faster networking FOSDEM 2022 6 February 2022 10