On Wed, May 3, 2017 at 5:50 AM, Andy Furniss wrote: > Andy Furniss wrote: > >> Andy Furniss wrote: >> >> b) it reacts to increase in RTT. An experiment with 10 Mbps bottleneck, >>>> 40 ms RTT and a typical 1000 packet buffer, increase >>>> in RTT with BBR is ~3 ms while with cubic it is over 1000 ms. >>>> >>> >>> That is a nice aspect (though at 60mbit hfsc + 80ms bfifo I tested >>> with 5 tcps it was IIRC 20ms vs 80 for cubic). I deliberately test >>> using ifb on my PC because I want to pretend to be a router - IME >>> (OK it was a while ago) testing on eth directly gives different >>> results - like the locally generated tcp is backing off and giving >>> different results. >>> >> >> I retested this with 40ms latency (netem) with hfsc + 1000 pfifo on >> ifb. >> > > So, as Jonathan pointed out to me in another thread bbr needs fq and it > seems fq only wotks on root of a real eth, which means thay are invalid > tests. > ​Specifically, BBR needs packet pacing to work properly: the algorithm depends on the packets being properly paced. Today, fq is the only qdisc supporting pacing. The right answer would be to add packet pacing to cake/fq_codel directly. Until that is done, we don't know how BBR will work in our world. - Jim​ > > I will soon (need to find a crossover cable!) be able to see using a > third sender how cake varies shaping bbr in simulated ingress. > > I can test now how bbr fills buffers - some slightly strange results, > one netperf ends up being "good" = buffer only a few ms. > > 5 netperfs started together are not so good but nothing like cubic. > > 5 netperfs started with a gap of a second or two are initially terrible, > filling the buffer for about 30 seconds, then eventually falling back to > lower occupancy. > > TODO - maybe this is a netperf artifact like bbr/fq thinks it is app > limited. > > The worse thing about bbr + longer RTT I see so far is that its design > seems to be to deliberately bork latency by 2x rtt during initial > bandwidth probe. It does drain afterwards, but for something like dash > generating a regular spike is not very game friendly and the spec > "boasts" that unlike cubic a loss in the exponential phase is ignored, > making ingress shaping somewhat less effective. > > _______________________________________________ > Cake mailing list > Cake@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/cake >