Subject: Re: [PATCH] Too aggressive cwnd backoff

From: Baruch Even <[email-masked]>
Date: Thu, 07 Apr 2005 19:14:45 +0100

Stephen Hemminger wrote:
> On Thu, 7 Apr 2005 19:41:46 +0300
> Baruch Even <[email-masked]> wrote:
>>The provided patch will set limit to tp->ssthresh. This was the original
>>behaviour in some older version of Linux.
> 
> I think this is a real problem, and was observed by Werner with umlsim.
> Don't know when it got introduced because it appears to pre-date the
> '04 work in adding Westwood, BIC, Vegas. Perhaps Alexey can shed some
> light on this.
> 
> Going back to the pre-westwood code in BK, the /2 is still there.

This wasn't there in 2.4.23 on which on the original work of H-TCP was 
done. I've encountered it in my work on the 2.6.6 version, but didn't 
understand all the implications at the time. I've re-encountered it now 
that I'm redoing the patches to 2.6.11, and it's as good a time as ever 
to resolve it.

The effect is not catastrophic, but it does mean that we leave recovery 
into slow-start like ascend of cwnd until we get to ssthresh again. It 
does mean that after recovery we inject a lot of packets to the network 
at a very fast rate.

Baruch