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Date: Fri, 16 Feb 2018 12:54:05 -0800
From: Eric Dumazet <edumazet@...gle.com>
To: Oleksandr Natalenko <oleksandr@...alenko.name>
Cc: Neal Cardwell <ncardwell@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>,
"David S. Miller" <davem@...emloft.net>,
Netdev <netdev@...r.kernel.org>,
Yuchung Cheng <ycheng@...gle.com>,
Soheil Hassas Yeganeh <soheil@...gle.com>,
Jerry Chu <hkchu@...gle.com>, Dave Taht <dave.taht@...il.com>
Subject: Re: TCP and BBR: reproducibly low cwnd and bandwidth
On Fri, Feb 16, 2018 at 9:25 AM, Oleksandr Natalenko
<oleksandr@...alenko.name> wrote:
> Hi.
>
> On pátek 16. února 2018 17:33:48 CET Neal Cardwell wrote:
>> Thanks for the detailed report! Yes, this sounds like an issue in BBR. We
>> have not run into this one in our team, but we will try to work with you to
>> fix this.
>>
>> Would you be able to take a sender-side tcpdump trace of the slow BBR
>> transfer ("v4.13 + BBR + fq_codel == Not OK")? Packet headers only would be
>> fine. Maybe something like:
>>
>> tcpdump -w /tmp/test.pcap -c1000000 -s 100 -i eth0 port $PORT
>
> So, going on with two real HW hosts. They are both running latest stock Arch
> Linux kernel (4.15.3-1-ARCH, CONFIG_PREEMPT=y, CONFIG_HZ=1000) and are
> interconnected with 1 Gbps link (via switch if that matters). Using iperf3,
> running each test for 20 seconds.
>
> Having BBR+fq_codel (or pfifo_fast, same result) on both hosts:
>
> Client to server: 112 Mbits/sec
> Server to client: 96.1 Mbits/sec
>
> Having BBR+fq on both hosts:
>
> Client to server: 347 Mbits/sec
> Server to client: 397 Mbits/sec
>
> Having YeAH+fq on both hosts:
> [1] https://natalenko.name/myfiles/bbr/
>
Something fishy really :
09:18:31.449903 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [P.],
seq 76745:79641, ack 38, win 227, options [nop,nop,TS val 2327043753
ecr 3190508870], length 2896
09:18:31.449916 IP 172.29.28.55.14936 > 172.29.28.1.5201: Flags [.],
ack 79641, win 1011, options [nop,nop,TS val 3190508870 ecr
2327043753], length 0
09:18:31.449925 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 79641:83985, ack 38, win 227, options [nop,nop,TS val 2327043753
ecr 3190508870], length 4344
09:18:31.449936 IP 172.29.28.55.14936 > 172.29.28.1.5201: Flags [.],
ack 83985, win 987, options [nop,nop,TS val 3190508870 ecr
2327043753], length 0
09:18:31.450112 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 83985:86881, ack 38, win 227, options [nop,nop,TS val 2327043753
ecr 3190508870], length 2896
09:18:31.450124 IP 172.29.28.55.14936 > 172.29.28.1.5201: Flags [.],
ack 86881, win 971, options [nop,nop,TS val 3190508871 ecr
2327043753], length 0
09:18:31.450299 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 86881:91225, ack 38, win 227, options [nop,nop,TS val 2327043753
ecr 3190508870], length 4344
09:18:31.450313 IP 172.29.28.55.14936 > 172.29.28.1.5201: Flags [.],
ack 91225, win 947, options [nop,nop,TS val 3190508871 ecr
2327043753], length 0
09:18:31.450491 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [P.],
seq 91225:92673, ack 38, win 227, options [nop,nop,TS val 2327043753
ecr 3190508870], length 1448
09:18:31.450505 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 92673:94121, ack 38, win 227, options [nop,nop,TS val 2327043753
ecr 3190508871], length 1448
09:18:31.450511 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [P.],
seq 94121:95569, ack 38, win 227, options [nop,nop,TS val 2327043754
ecr 3190508871], length 1448
09:18:31.450720 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 95569:101361, ack 38, win 227, options [nop,nop,TS val 2327043754
ecr 3190508871], length 5792
09:18:31.450932 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 101361:105705, ack 38, win 227, options [nop,nop,TS val 2327043754
ecr 3190508871], length 4344
09:18:31.451132 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 105705:110049, ack 38, win 227, options [nop,nop,TS val 2327043754
ecr 3190508871], length 4344
09:18:31.451342 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 110049:111497, ack 38, win 227, options [nop,nop,TS val 2327043754
ecr 3190508871], length 1448
09:18:31.455841 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 111497:112945, ack 38, win 227, options [nop,nop,TS val 2327043759
ecr 3190508871], length 1448
Not only the receiver suddenly adds a 25 ms delay, but also note that
it acknowledges all prior segments (ack 112949), but with a wrong ecr
value ( 2327043753 )
instead of 2327043759
09:18:31.482238 IP 172.29.28.55.14936 > 172.29.28.1.5201: Flags [.],
ack 112945, win 1111, options [nop,nop,TS val 3190508903 ecr
2327043753], length 0
09:18:31.482704 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 112945:114393, ack 38, win 227, options [nop,nop,TS val 2327043786
ecr 3190508903], length 1448
09:18:31.482734 IP 172.29.28.55.14936 > 172.29.28.1.5201: Flags [.],
ack 114393, win 1134, options [nop,nop,TS val 3190508903 ecr
2327043786], length 0
09:18:31.482802 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 114393:117289, ack 38, win 227, options [nop,nop,TS val 2327043786
ecr 3190508903], length 2896
09:18:31.482813 IP 172.29.28.55.14936 > 172.29.28.1.5201: Flags [.],
ack 117289, win 1179, options [nop,nop,TS val 3190508903 ecr
2327043786], length 0
09:18:31.483138 IP 172.29.28.1.5201 > 172.29.28.55.14936: Flags [.],
seq 117289:120185, ack 38, win 227, options [nop,nop,TS val 2327043786
ecr 3190508903], length 2896
09:18:31.483158 IP 172.29.28.55.14936 > 172.29.28.1.5201: Flags [.],
ack 120185, win 1224, options [nop,nop,TS val 3190508904 ecr
2327043786], length 0
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