[fpoling]

One non-trivial problem with async in Rust is that it leads to code that allocates on one CPU and free memory on another. That kills a lot of optimizations that system allocators try to do with CPU local caching and harms performance badly especially on fat servers with a lot of CPUs. When one hits this problem, there is no easy solution.

Ideally using an allocator per request would solve this issue, but Rust has no real support for it.

A workaround that works is to stop using async and just use a native thread per request. But then most crates and frameworks these days use async. So indeed async abstraction us very leaky regarding the cost.