I don't believe codel does start fresh; there are various back-off mechanisms that have been employed in the management of 'count' such that if the drop state is entered soon after it previously left the drop state, it'll re-enter at close to the same interval.
I believe these mechanisms were put in place to combat the sluggishness, but that doesn't help the initial drop state. In practice, I've found that incrementing 'count' more rapidly can help to a point... but incrementing it too much appears to result in the sqrt approximation diverging from the ideal value, and then things start to fall apart. --Jeff ________________________________________ From: aqm [[email protected]] on behalf of Polina Goltsman [[email protected]] Sent: Wednesday, September 30, 2015 11:43 AM To: Bob Briscoe Cc: AQM IETF list Subject: Re: [aqm] CoDel's control law that determines drop frequency Bob, May I ask how curvy red is supposed to perform in those situations? If I understand Codel's law correctly, Codel "starts fresh" every time it enters dropping state, so when the load increases it will take more time for the control law to reach the correct "count" value for the queue to drop. Thus with higher load latency is increased. Now, if I understood your curvey red report correctly, you argued that AQM should increase latency when load increases since otherwise it will cause too much loss. Which makes Codel's behavior at least justified ... BTW, I haven't seen any place in the original specification that suggested that fixed target delay is the intended design goal. Does this make any sense? Regards, Polina On 09/30/2015 02:59 PM, Bob Briscoe wrote: > Polina, > > I think this was it: > <https://www.ietf.org/proceedings/85/slides/slides-85-iccrg-2.pdf> > > I have a set of charts from Rong with many more tests showing CoDel's > sluggish responsiveness, but I believe the above was the published > summary. > > > Bob > > On 30/09/15 10:13, Polina Goltsman wrote: >> Dear Bob, >> >> On 09/30/2015 10:50 AM, Bob Briscoe wrote: >>> >>> Early on, Rong Pan showed that it takes CoDel ages to bring high >>> load under control. I think this linear increase is the reason. >> >> Is there a link to this ? >> >> Polina >> >> _______________________________________________ >> aqm mailing list >> [email protected] >> https://www.ietf.org/mailman/listinfo/aqm > _______________________________________________ aqm mailing list [email protected] https://www.ietf.org/mailman/listinfo/aqm _______________________________________________ aqm mailing list [email protected] https://www.ietf.org/mailman/listinfo/aqm
