Re: [Bloat] AQM and PPP on Linux

[Eric Dumazet <eric.dumazet@gmail.com>]

On Tue, 2015-07-28 at 16:49 +0200, Eric Dumazet wrote:
> On Tue, 2015-07-28 at 07:31 -0700, Simon Barber wrote:
> > The issue is that Codel tries to keep the delay low, and will start 
> > dropping when sojourn time grows above 5ms for 100ms. For longer RTT links 
> > more delay is necessary to avoid underutilizing the link. This is due to 
> > the multiplicative decrease - it's worst with Reno, where the halving of 
> > cWind means that you need to have a full BDP of data in the buffer to avoid 
> > the link going idle when cWind is halved. With longer RTTs this means more 
> > delay than Codel allows is required to avoid a throughput hit. The worst 
> > case happens when a single flow is controlled, but that can be a common 
> > situation. My proposal is to sense and have the target value in Codel 
> > automatically adjust when this worst case scenario happens - which would 
> > mitigate most of the downside.
> 
> As I said, I've never seen what you describe.
> 
> 100ms value is not a go/nogo threshold. It is a hint, based on real
> world values. We are speaking of 100 ms sojourn time in the CoDel queue,

typo : 5 ms ( codel target )