LPC2018 - XDP 1.5 Years In Production. Evolution and Lessons Learned.





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Published on Dec 3, 2018

url: https://linuxplumbersconf.org/event/2...
speaker: Nikita V. Shirokov (Facebook)

Today every packet which is reaching Facebook’s network is being processed by XDP enabled application. We have been using it for more then 1.5 years and this talk is about evolution of XDP and BPF which has been driven by our production needs. I’m going to talk about history of changes in core BPF components as well as will show why and how it was done. What performance improvements did we get (with synthetics and real world data) and how it was implemented. Also I’m going to talk about issues and shortcoming of BPF/XDP which we have found during our operations, as well as some gotchas and corner cases. In the end we are going to discuss on what is still missing and which part could be improved.

Topics and areas of existing BPF/XDP infrastructure which are going to be covered in this talk:

why helpers such as bpf_adjust_head/bpf_adjust_tail has been added
unittesting and microbenchmarking with bpf_prog_test_run: how to add test coverage of you BPF program and track the regression (we are going to cover how spectre affected BPF kernel infrastructure and what tweaks has been made to get some performance back)
how map-in-map helps us to scale and make sure that we don't waste memory
NUMA aware allocation for BPF maps
inline lookups for BPF arrays/map-in-map
Lessons which we have learned during operation of XDP:

BPF instruction counts vs complexity
How to attach more then one XDP program to the interface
when LLVM and verifier are not the same: some tricks to force LLVM to generate proper BPF
we will briefly discuss HW limitation: NIC's bandwidth vs packet per second performance
Missing parts: what and why could be added:

the need for hardware checksumming offload
bounded loops: what they would allow us to do


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