Re: [aqm] CoDel's control law that determines drop frequency
Polina Goltsman <polina.goltsman@student.kit.edu> Wed, 30 September 2015 16:37 UTC
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Date: Wed, 30 Sep 2015 18:37:14 +0200
From: Polina Goltsman <polina.goltsman@student.kit.edu>
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To: Jeff Weeks <jweeks@sandvine.com>, Bob Briscoe <ietf@bobbriscoe.net>
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Subject: Re: [aqm] CoDel's control law that determines drop frequency
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It seems that the presentation used Linux version for Codel. I can't quite get what exactly it does but it does not decrease count by two (as in the draft): on reentering dropping state within 16 intervals: delta = vars->count - vars->lastcount; vars->count = delta; vars->lastcount = vars->count; See the bottom image on slide 18 https://www.ietf.org/proceedings/85/slides/slides-85-iccrg-2.pdf: count does not get reset to zero, but it drops by at least two times * . It also seems that the delay variations on slide 15 with two UDP flows were caused by this reentering behavior... * cake version did not exist at the time, did it? On 09/30/2015 05:57 PM, Jeff Weeks wrote: > 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 [aqm-bounces@ietf.org] on behalf of Polina Goltsman [polina.goltsman@student.kit.edu] > 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 >>> aqm@ietf.org >>> https://www.ietf.org/mailman/listinfo/aqm > _______________________________________________ > aqm mailing list > aqm@ietf.org > https://www.ietf.org/mailman/listinfo/aqm
- [aqm] CoDel's control law that determines drop fr… Bob Briscoe
- Re: [aqm] CoDel's control law that determines dro… Toke Høiland-Jørgensen
- Re: [aqm] CoDel's control law that determines dro… Bob Briscoe
- Re: [aqm] CoDel's control law that determines dro… Andrew Mcgregor
- Re: [aqm] CoDel's control law that determines dro… Bob Briscoe
- Re: [aqm] CoDel's control law that determines dro… Dave Taht
- Re: [aqm] CoDel's control law that determines dro… Jonathan Morton
- Re: [aqm] CoDel's control law that determines dro… Polina Goltsman
- Re: [aqm] CoDel's control law that determines dro… Toke Høiland-Jørgensen
- Re: [aqm] CoDel's control law that determines dro… Bless, Roland (TM)
- Re: [aqm] CoDel's control law that determines dro… Toke Høiland-Jørgensen
- Re: [aqm] CoDel's control law that determines dro… Bob Briscoe
- Re: [aqm] CoDel's control law that determines dro… Bob Briscoe
- Re: [aqm] CoDel's control law that determines dro… Bless, Roland (TM)
- Re: [aqm] CoDel's control law that determines dro… Bob Briscoe
- Re: [aqm] CoDel's control law that determines dro… Kuhn Nicolas
- Re: [aqm] CoDel's control law that determines dro… Polina Goltsman
- Re: [aqm] CoDel's control law that determines dro… Jeff Weeks
- Re: [aqm] CoDel's control law that determines dro… Polina Goltsman
- Re: [aqm] CoDel's control law that determines dro… Bob Briscoe
- Re: [aqm] CoDel's control law that determines dro… Jeff Weeks
- Re: [aqm] CoDel's control law that determines dro… Dave Dolson
- Re: [aqm] CoDel's control law that determines dro… Andrew Mcgregor
- Re: [aqm] CoDel's control law that determines dro… Jeff Weeks
- Re: [aqm] CoDel's control law that determines dro… Dave Taht
- Re: [aqm] CoDel's control law that determines dro… Jonathan Morton