On Wed, Jan 25, 2017 at 5:38 PM, Hans-Kristian Bakke wrote: > Actually.. the 1-4 mbit/s results with fq sporadically appears again as I > keep testing but it is most likely caused by all the unknowns between me an > my testserver. But still, changing to pfifo_qdisc seems to normalize the > throughput again with BBR, could this be one of those times where BBR and > pacing actually is getting hurt for playing nice in some very variable > bottleneck on the way? > Possibly. Would you be able to take a tcpdump trace of each trial (headers only would be ideal), and post on a web site somewhere a pcap trace for one of the slow trials? For example: tcpdump -n -w /tmp/out.pcap -s 120 -i eth0 -c 1000000 & thanks, neal > > On 25 January 2017 at 23:01, Neal Cardwell wrote: > >> On Wed, Jan 25, 2017 at 3:54 PM, Hans-Kristian Bakke >> wrote: >> >>> Hi >>> >>> Kernel 4.9 finally landed in Debian testing so I could finally test BBR >>> in a real life environment that I have struggled with getting any kind of >>> performance out of. >>> >>> The challenge at hand is UDP based OpenVPN through europe at around 35 >>> ms rtt to my VPN-provider with plenty of available bandwith available in >>> both ends and everything completely unknown in between. After tuning the >>> UDP-buffers up to make room for my 500 mbit/s symmetrical bandwith at 35 ms >>> the download part seemed to work nicely at an unreliable 150 to 300 mbit/s, >>> while the upload was stuck at 30 to 60 mbit/s. >>> >>> Just by activating BBR the bandwith instantly shot up to around 150 >>> mbit/s using a fat tcp test to a public iperf3 server located near my VPN >>> exit point in the Netherlands. Replace BBR with qubic again and the >>> performance is once again all over the place ranging from very bad to bad, >>> but never better than 1/3 of BBRs "steady state". In other words "instant >>> WIN!" >>> >> >> Glad to hear it. Thanks for the test report! >> >> >>> However, seeing the requirement of fq and pacing for BBR and noticing >>> that I am running pfifo_fast within a VM with virtio NIC on a Proxmox VE >>> host with fq_codel on all physical interfaces, I was surprised to see that >>> it worked so well. >>> I then replaced pfifo_fast with fq and the performance went right down >>> to only 1-4 mbit/s from around 150 mbit/s. Removing the fq again regained >>> the performance at once. >>> >>> I have got some questions to you guys that know a lot more than me about >>> these things: >>> >> 1. Do fq (and fq_codel) even work reliably in a VM? What is the best >>> choice for default qdisc to use in a VM in general? >>> >> >> Eric covered this one. We are not aware of specific issues with fq in VM >> environments. And we have tested that fq works sufficiently well on Google >> Cloud VMs. >> >> >>> 2. Why do BBR immediately "fix" all my issues with upload through that >>> "unreliable" big BDP link with pfifo_fast when fq pacing is a requirement? >>> >> >> For BBR, pacing is part of the design in order to make BBR more "gentle" >> in terms of the rate at which it sends, in order to put less pressure on >> buffers and keep packet loss lower. This is particularly important when a >> BBR flow is restarting from idle. In this case BBR starts with a full cwnd, >> and it counts on pacing to pace out the packets at the estimated bandwidth, >> so that the queue can stay relatively short and yet the pipe can be filled >> immediately. >> >> Running BBR without pacing makes BBR more aggressive, particularly in >> restarting from idle, but also in the steady state, where BBR tries to use >> pacing to keep the queue short. >> >> For bulk transfer tests with one flow, running BBR without pacing will >> likely cause higher queues and loss rates at the bottleneck, which may >> negatively impact other traffic sharing that bottleneck. >> >> >>> 3. Could fq_codel on the physical host be the reason that it still works? >>> >> >> Nope, fq_codel does not implement pacing. >> >> >>> 4. Do BBR _only_ work with fq pacing or could fq_codel be used as a >>> replacement? >>> >> >> Nope, BBR needs pacing to work correctly, and currently fq is the only >> Linux qdisc that implements pacing. >> >> >>> 5. Is BBR perhaps modified to do the right thing without having to >>> change the qdisc in the current kernel 4.9? >>> >> >> Nope. Linux 4.9 contains the initial public release of BBR from September >> 2016. And there have been no code changes since then (just expanded >> comments). >> >> Thanks for the test report! >> >> neal >> >> >