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🤣🐧🤡 This would not even be an issue if everyone hadn't jumped on the epoll 🤡🚗

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May 1, 2021

I'm not surprised to find out that Linux kernel socket load balancing is in a terrible state with no good options. Some background: blog.cloudflare.com/the-sad-state- Traditional epoll wakes every thread and they race to accept the connection. EPOLLEXCLUSIVE fixes it but uses LIFO order.

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The Linux kernel didn't really provide other viable options. The least bad option not requiring patching the kernel is probably REUSEPORT combined with dealing with the BPF nonsense they expect you to do. You still use epoll but with a socket per worker instead of sharing one.

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Blocking accept uses FIFO rather than LIFO, but has other issues. It requires a weird non-standard approach to properly handle graceful reloads, etc. It doesn't really make any sense that EPOLLEXCLUSIVE uses a different order than blocking accept by default. It's a weird choice.

12:30 AM · May 2, 2021Twitter Web App

Kumar Kartikeya Dwivedi

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IIRC I think it had something to do with LIFO favoring workers that were "cache hot", but then my guess is that also means those threads get more wakeups and overall concurrency is limited as a result.

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LIFO is lower overhead under very low load. If you have high load, there are no cold workers. The nginx model is to make one worker per CPU core. On many high performance systems, those will even be pinned to cores. It wants to have even load balancing across those threads/CPUs.

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