Similarly, how many queues would be required when hundreds or thousands of users share a 1Gbps link? It seems that fq_codel is tuned for a single host or residential gateway. Has anyone investigate this?
-----Original Message----- From: aqm [mailto:[email protected]] On Behalf Of Simon Barber Sent: Tuesday, June 09, 2015 1:14 PM To: Jonathan Morton; Steven Blake Cc: [email protected] Subject: Re: [aqm] CoDel on high-speed links My concern with fq_codel is that by putting single flows into single Codel instances you hit the problem with Codel where it limits bandwidth on higher RTT paths. Simon Sent with AquaMail for Android http://www.aqua-mail.com On June 9, 2015 9:32:15 AM Jonathan Morton <[email protected]> wrote: > > > On 9 Jun, 2015, at 19:11, Steven Blake <[email protected]> wrote: > > > > On a 10 GE link > > serving 2.5 MPPs on average, CoDel would only drop 0.013% of packets > > after 1000 drops (which would occur after 6.18 secs). This doesn't seem > > to be very effective. > > Question: have you worked out what drop rate is required to achieve control > of a TCP at that speed? There are well-known formulae for standard TCPs, > particularly Reno. You might be surprised by the result. > > Fundamentally, Codel operates on the principle that one mark/drop per RTT > per flow is sufficient to control a TCP, or a flow which behaves like a > TCP; *not* a particular percentage of packets. This is because TCPs are > generally required to perform multiplicative decrease upon a *single* > congestion event. The increasing count over time is meant to adapt to > higher flow counts and lower RTTs. Other types of flows tend to be sparse > and unresponsive in general, and must be controlled using some harder > mechanism if necessary. > > One such mechanism is to combine Codel with an FQ system, which is exactly > what fq_codel in Linux does. Fq_codel has been tested successfully at > 10Gbps. Codel then operates separately for each flow, and unresponsive > flows are isolated. > > - Jonathan Morton > > _______________________________________________ > 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
