I don't think any web server gets to this level of control on the tcp/ip level, this is something that should be addressed in the OS' network stack.

Unless you have an exokernel operating system.

Nah, that's not even necessary, I believe: the congestion window is a TCP feature, but any normal user space program (with a few privileges) can create IP datagrams with custom content, so you would only need to implement a bit of tcp in a normal old style monolithic kernel

And since you control the only higher level protocol (your http implementation) you can probably cut some corners and get done quickly :)

You may be able to create them, but as a server, how would you receive incoming connections?

No need for an exokernel here. A microkernel could enable the same thing, since your network stack would be Yet Another Service (TM). This could easily be implemented on the likes of L4.

I don't really see the difference between patching the kernel and patching the privileged network stack server in a microkernel environment.

In an exokernel environment, the network stack server wouldn't be privileged.

It's not tunable at the app level. On linux it requires a kernel patch to change. I'm not sure about other OS's.

I wish there was a patch where you could enable it on linux via a ioctl/setsockopt. Would be very useful to those of us who aren't google.

Edit:

I wished, google already sent the patch in May for this:

http://www.amailbox.org/mailarchive/linux-netdev/2010/5/26/6...

Nice!

something like: ip route change default via 0.0.0.0 dev eth0 initcwnd 10

Perhaps "ip route change default via <your gateway address> dev eth0 initcwnd 10" -- your gateway address, not 0.0.0.0.

That doesn't seem to work for me:

    RTNETLINK answers: No such file or directory

Apparently I need to patch my kernel?

slight offtopic: that's one of my favorite error messages that is actually relatively common.