Thread by @TerribleQuant

Multithreading is not an instant speed booster:

A word on these three:

Async I/O
Multi-threaded CPU tasks
Hyper-threaded CPU tasks

Async I/O will only benefit speed-wise from the writing data component of the work and can slow you down if that is not significant. There is only one NAC remember, but there is not infinite cache and management is expensive.

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Multi-threading is great, but not for file handling, that won't be faster and will split your cache once again so for ultra low latency applications you usually just have one super fast core enabled so you can maximise cache.

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Hyper threading (thread per logical instead of core) can do +50% for some tasks, but -50% for others. Again it's all about the cache and the duration of the task (i.e. time to make and manage threads). Use the data structure wisely.

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