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diff --git a/docs/content/methodology/test/reassembly.md b/docs/content/methodology/test/reassembly.md new file mode 100644 index 0000000000..61064d1bbc --- /dev/null +++ b/docs/content/methodology/test/reassembly.md @@ -0,0 +1,48 @@ +--- +title: "Reassembly" +weight: 10 +--- + +# Packet reassembly performance + +IP protocols (mainly IPv4) specify conditions for packet fragmentation +and packet reassembly. For VPP, the reassembly operation is more CPU intensive. +By default, VPP avoids unnecessary work, so there are only few scenarios +where VPP fragments IP packets, and even less scenarios where it reassemblies +the fragmented packets. + +The typical situation when fragmentation is performed occurs with +tunnel encapsulation protocols, when the packet after encapsulation +would not fit into interface MTU (maximum transmission unit). +Some, but not all, encapsulation protocols also require +packet reassembly for decapsulation. + +As the search algorithms used in CSIT work best when the number of packets +coming from TG (traffic generator) is the same +as the number of packets expected to come back to TG, +the easiest way to test reassembly performance of VPP is using +a 3-node testbed and a tunneling test suite adapted to cause fragmentation. + +## MTU + +By default, testbeds in CSIT are configured with MTU high enough +for encapsulated packets to fit in. +Not all devices and drivers used by VPP do support lowering MTU value. +For reassembly tests, only the physical interfaces on the DUT1-DUT2 link +have lowered MTU, and that currently works only with dpdk plugin. + +## Impacts + +Reassembly suites with small number of flows and tunnels +usually place encapsulation+fragmentation and reassembly+decapsulation +on different workers, so the bottleneck seen in performance results +is not affected by fragmentation performance. + +Reassembly suites with high number of flows and tunnels +achieve balanced load on all workers, so their overall performance +is affected by both fragmentation and reassembly performance. + +Some protocols (e.g. IPsec) are CPU intensive not only +on fragmentation and reassembly, but also on encapsulation and decapsulation. +Reassembly (and depending on scale also fragmentation) impact +on those tests can still be visible, at least for big regressions. |