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how do i get lowest possible datagram latency on Linux these days? io_uring? dpdk? raw sockets? running a kernel with real time patches (recent NixOS boot.kernelPackages = pkgs.linuxPackages-rt) dedicated machines, dedicated gigabit ethernet link(s), rt scheduling (jack audio)

Tom Schouten

@tom_zwizwa

Aug 28

looking into dpdk it seems that this could in principle be used for hard real time applications dedicated cores interact with nics directly using shared memory (dram or cache) and cores uses polling receive

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the absolute lowest latency answer is use a smart nic, the second lowest latency is run in a kernel thread, after that is probably cpu affinity and io_uring. though it also matters whether you're talking about worst-case, average, or 90th percentile

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for worst case you need to worry about the scheduler

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mostly interested in worst case in the order of 1ms. this is for sending real time audio

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intel e1000 seems to be supported in DPDK so basically if i do UDP or raw Ethernet this shouldn't be too hard to try out... the NIC doesn't need to do anything smart i think?

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I haven't used dpdk but I've heard only bad things.

@sargun

is a good person to ask

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Exactly the kind of thing I'm looking for before diving in. Bad in what sense?

5:57 PM · Aug 28, 2022Twitter Web App

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DPDK is basically a framework for writing a "unikernel" for packet processing. ...The unfortunate part is that you're effectively having to co-exist with Linux. That includes the scheduler, other tasks, etc...

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I'd actually strongly suggest XDP with a userspace ring buffer, instead of DPDK.

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