[masklinn]

> I can see why they rewrote QUIC in Rust and for use in userspace

As far as I know, while they might have either way, they did not ("rewrite QUICK [...] for use in userspace"): the linux kernel implementation only landed late 2025. Quiche was started ca 2018 (that's when Cloudflare started beta-deploying QUIC, the first public alpha of quiche was january 2019).

I don't know that there even was an in-kernel implementation of quic before msquic.sys which I believe first shipped in Server 2022 circa mid 2021 (and is used as the implementation backend by MsQuic on Server 2022 and W11).

[benmmurphy]

I think the original commenter confused taking the CUBIC implementation from the kernel and rewriting that in Rust for use in their QUIC implementation or they just jumbled their wording. It does make sense to use an existing battle tested implementation of a congestion algorithm because there are potential many real world failure modes that you might not anticipate if you try and write an implementation from scratch.

[neuralkoi]

Yes, I meant CUBIC implementation! But I'm glad I made the mistake-I learned some interesting things from the responses above.