dnsdist: Random load-balancing of incoming queries on reuseport sockets #13399
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When `SO_ATTACH_REUSEPORT_EBPF` is available (Linux >= 4.6) along with `BPF_FUNC_get_prandom_u32()` (Linux >= 4.1), this implements a fully random load-balancing policy between incoming sockets in the same `reuseport` group (listening address and port, `reuseport` set). This is needed because Linux implements `reuseport` load-balancing based on (source IP, source port, destination IP, destination port, protocol), which means that if all queries comes from the same IP and port, and to the same IP and port, they will be distributed to a single worker only, using a single CPU core.
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| { | ||
| #if defined(HAVE_BPF_FUNC_get_prandom_u32) && defined(SO_ATTACH_REUSEPORT_EBPF) | ||
| const struct bpf_insn randomReusePortPolicy[] = { | ||
| #include "random-reuseport-policy.ebpf" |
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IMO, this would be a valuable function to have in the recursor. |
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Short description
When
SO_ATTACH_REUSEPORT_EBPFis available (Linux >= 4.6) along withBPF_FUNC_get_prandom_u32()(Linux >= 4.1), this implements a fully random load-balancing policy between incoming sockets in the samereuseportgroup (listening address and port,reuseportset). This is needed because Linux implementsreuseportload-balancing based on (source IP, source port, destination IP, destination port, protocol), which means that if all queries comes from the same IP and port, and to the same IP and port, they will be distributed to a single worker only, using a single CPU core.This is a draft pull request to get feedback (@wojas). The current eBPF code is very simple, and is not optimized for NUMA nodes or even just to keep the queries on the local CPU cores, which would be possible. @omoerbeek, @Habbie, if you are interested in using that code in the authoritative server and/or the recursor I'll refactor the eBPF loading code to make it possible.
Note that it is actually possible to replace the eBPF policy from an external program at runtime, but then we need to find a way to let the program know how many sockets we have, and perhaps our CPU affinity. eBPF maps could probably be used to do that.
Related to #8033 and #13327.
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