[lxgr]

> Why do the hard work if the same thing can be done by the kernel, or even by the card itself?

How would you swap out the TCP congestion control algorithm in an OS, or even hardware, you don't control?

> Drown other applications for your own benefit?

Fairness equivalent to classic TCP is a design goal of practically all alternative algorithms, so I'm not sure what you're implying.

It's entirely possible to improve responsivity without compromising on fairness, as e.g. BBR has shown.

[neilalexander]

> How would you swap out the TCP congestion control algorithm in an OS, or even hardware, you don't control?

On the contrary, introducing their own novel/mysterious/poorly implemented congestion control algorithms is not a thing I want userspace applications doing.

[lxgr]

Fortunately you don't get any say in what my userspace applications do on my own hardware.

And if you worry about hostile applications on your own hardware, the OS is an excellent point to limit what they can do – including overwhelming your network interface.

[neilalexander]

> the OS is an excellent point to limit what they can do – including overwhelming your network interface

One might even call this "congestion control"!

[lxgr]

No, congestion control in the network sense is about congestion at choke points in packet networks due to higher inflow than outflow rates.

While you're still on your own host, your OS has complete visibility into which applications are currently intending to send data and can schedule them much more directly.