Re: [RFC] TCP congestion schedulers

[John Heffner <jheffner@xxxxxxx>]

On Sat, 19 Mar 2005, Andi Kleen wrote:

> Stephen Hemminger <shemminger@xxxxxxxx> writes:
>
> > Since developers want to experiment with different congestion
> > control mechanisms, and the kernel is getting bloated with overlapping
> > data structure and code for multiple algorithms; here is a patch to
> > split out the Reno, Vegas, Westwood, BIC congestion control stuff
> > into an infrastructure similar to the I/O schedulers.
>
> [...]
>
> Did you do any benchmarks to check that wont slow it down?
>
> I would recommend to try it on a IA64 machine if possible. In the
> past we found that adding indirect function calls on IA64 to networking
> caused measurable slowdowns in macrobenchmarks.
> In that case it was LSM callbacks, but your code looks like it will
> add even more.

Is there a canonical benchmark?

Would you really expect a single extra indirect call per ack to have a
significant performance impact?  This is surprising to me.  Where does the
cost come from?  Replacing instruction cache lines?

  -John