Re: [PATCH] TCP-Hybla proposal

Stephen Hemminger
2005-02-23T04:22:51Z

> On Tue, 22 Feb 2005 10:14:47 -0800, David S. Miller <davem@davemloft.net> wrote:
>
>>> On Tue, 22 Feb 2005 13:03:11 -0500 (EST)
>>> John Heffner <jheffner@psc.edu> wrote:
>>>
>>
>>>> > An idea I've been toying with for a while now is completely abstracting
>>>> > congestion control. Then you could have congestion control loadable
>>>> > modules, which would avoid this mess of experimental algorithms inside the
>>>> > main-line kernel. If done right, they might be able to work seamlessly
>>>> > with SCTP, too. The tricky part is making sure the interface is complete
>>>> > enough.
There might be a noticeable performance impact to making it truly
modular. Calling a function in a module is slower. In some tests, I see
a 5 to 10% drop in performance when Ethernet driver is a module versus
builtin.

You might want to look at how the I/O schedulers are configured as an
example.

>>>
>>> The symbols exported to allow this would need to be EXPORT_SYMBOL_GPL().
>
>
> Why's that?

Because the kernel developers who hold the collective copyright on the
existing GPL TCP code do not want some vendor producing a closed source
binary module of "enhanced TCP".