Re: [PATCH] TCP-Hybla proposal

[Stephen Hemminger]

> On Tue, 22 Feb 2005 10:14:47 -0800, David S. Miller <davem@xxxxxxxxxxxxx> wrote:
>
> > > On Tue, 22 Feb 2005 13:03:11 -0500 (EST)
> > > John Heffner <jheffner@xxxxxxx> 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".
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