Re: [RFC] TCP limited slow start

[John Heffner <jheffner@psc.edu>]

Stephen Hemminger wrote:
> Rolled my sleeve's up and gave this a try...
> 
> This is a implementation of Sally Floyd's Limited Slow Start
> for Large Congestion Windows.

Limited slow start is useful as a work-around for bottleneck queues that 
are inappropriately short.  I don't think it's good to run it all the 
time by default (with a max_ssthresh < infinity), because it slows down 
flows on healthy paths, and introduces another non-scalable parameter to 
TCP.

I see it as potentially useful as a per-route parameter, where you set 
it deliberately to work around some known problematic path.  A sysctl 
with a default value of infinity might be okay as well.

Practically speaking, we've had this in the Web100 patch for a long time 
(and still do, look for WAD_MaxSsthresh), but I've never found it all 
that useful.  If the bottleneck queue is too short, you usually end up 
getting screwed other ways too.

   -John