Re: TCP reaching to maximum throughput after a long time

[Yuchung Cheng]

On Tue, Apr 12, 2016 at 7:52 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>
> On Tue, 2016-04-12 at 12:17 +0000, Machani, Yaniv wrote:
> > Hi,
> > After updating from Kernel 3.14 to Kernel 4.4 we have seen a TCP performance degradation over Wi-Fi.
> > In 3.14 kernel, TCP got to its max throughout after less than a second, while in the 4.4  it is taking ~20-30 seconds.
> > UDP TX/RX and TCP RX performance is as expected.
> > We are using a Beagle Bone Black and a WiLink8 device.
> >
> > Were there any related changes that might cause such behavior ?
> > Kernel configuration and sysctl values were compared, but no significant differences have been found.
> >
> > See a log of the behavior below :
> > -----------------------------------------------------------
> > Client connecting to 10.2.46.5, TCP port 5001
> > TCP window size:  320 KByte (WARNING: requested  256 KByte)
> > ------------------------------------------------------------
> > [  3] local 10.2.46.6 port 49282 connected with 10.2.46.5 port 5001
> > [ ID] Interval       Transfer     Bandwidth
> > [  3]  0.0- 1.0 sec  5.75 MBytes  48.2 Mbits/sec
> > [  3]  1.0- 2.0 sec  6.50 MBytes  54.5 Mbits/sec
> > [  3]  2.0- 3.0 sec  6.50 MBytes  54.5 Mbits/sec
> > [  3]  3.0- 4.0 sec  6.50 MBytes  54.5 Mbits/sec
> > [  3]  4.0- 5.0 sec  6.75 MBytes  56.6 Mbits/sec
> > [  3]  5.0- 6.0 sec  3.38 MBytes  28.3 Mbits/sec
> > [  3]  6.0- 7.0 sec  6.38 MBytes  53.5 Mbits/sec
> > [  3]  7.0- 8.0 sec  6.88 MBytes  57.7 Mbits/sec
> > [  3]  8.0- 9.0 sec  7.12 MBytes  59.8 Mbits/sec
> > [  3]  9.0-10.0 sec  7.12 MBytes  59.8 Mbits/sec
> > [  3] 10.0-11.0 sec  7.12 MBytes  59.8 Mbits/sec
> > [  3] 11.0-12.0 sec  7.25 MBytes  60.8 Mbits/sec
> > [  3] 12.0-13.0 sec  7.12 MBytes  59.8 Mbits/sec
> > [  3] 13.0-14.0 sec  7.25 MBytes  60.8 Mbits/sec
> > [  3] 14.0-15.0 sec  7.62 MBytes  64.0 Mbits/sec
> > [  3] 15.0-16.0 sec  7.88 MBytes  66.1 Mbits/sec
> > [  3] 16.0-17.0 sec  8.12 MBytes  68.2 Mbits/sec
> > [  3] 17.0-18.0 sec  8.25 MBytes  69.2 Mbits/sec
> > [  3] 18.0-19.0 sec  8.50 MBytes  71.3 Mbits/sec
> > [  3] 19.0-20.0 sec  8.88 MBytes  74.4 Mbits/sec
> > [  3] 20.0-21.0 sec  8.75 MBytes  73.4 Mbits/sec
> > [  3] 21.0-22.0 sec  8.62 MBytes  72.4 Mbits/sec
> > [  3] 22.0-23.0 sec  8.75 MBytes  73.4 Mbits/sec
> > [  3] 23.0-24.0 sec  8.50 MBytes  71.3 Mbits/sec
> > [  3] 24.0-25.0 sec  8.62 MBytes  72.4 Mbits/sec
> > [  3] 25.0-26.0 sec  8.62 MBytes  72.4 Mbits/sec
> > [  3] 26.0-27.0 sec  8.62 MBytes  72.4 Mbits/sec
> >
>
> CC netdev, where this is better discussed.
>
> This could be a lot of different factors, and caused by a sender
> problem, a receiver problem, ...
>
> TCP behavior depends on the drivers, so maybe a change there can explain
> this.
>
> You could capture the first 5000 frames of the flow and post the pcap ?
> (-s 128 to capture only the headers)
pcap would be really helpful indeed. if possible please capture on
both 4.4 and 3.14 kernels.

>
> tcpdump -p -s 128 -i eth0 -c 5000 host 10.2.46.5 -w flow.pcap
>
>
> Also, while test is running, you could fetch
> ss -temoi dst 10.2.46.5:5001
>
>
>
>
>