netdev - Re: One way TCP bottleneck over 6 x Gbit tecl aggregated link // Kernel issue

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Date:	Thu, 26 Mar 2015 20:34:05 +0100
From:	Wolfgang Rosner <wrosner@...net.de>
To:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Subject: Re: One way TCP bottleneck over 6 x Gbit tecl aggregated link // Kernel issue

Hello, Eric

Am Montag, 23. März 2015 03:33:17 schrieben Sie:
> On Mon, 2015-03-23 at 01:57 +0100, Wolfgang Rosner wrote:
> > Are you ready to assist me on this track?
>
> First check if the problem is already solved, using this git tree ?
>
> http://git.kernel.org/cgit/linux/kernel/git/davem/net.git


Does not look like that :-(



I tried both 3.19.2 frome kernel.org and 
a git clone frome above adress from "master" this morning.
$ uname -a
Linux cruncher 4.0.0-rc5+ #1 SMP Thu Mar 26 08:48:08 CET 2015 x86_64 GNU/Linux


Sorry when it took some time.

I've built a workaround for my aufs nfsroot to get rid of that, at least for 
testing.
Both kernels were built w/o aufs patches, so we cannot blame this anymore
(I've learned that people like to do so...)


-----------

I tried sequential run to check for jitter and to allow for adaptation

for i in `seq 10` ; do  iperf -c 192.168.130.225 -t 100 ; done

3.17 / 3.30 / 3.16 / 3.19 / 3.29 / 3.29 / 3.35 / 3.32 / 3.22 / 3.32
Gbits/sec

...full bandwith at shared Link utilisation:

[  4]  0.0-10.0 sec  3.31 GBytes  2.84 Gbits/sec
[  3]  0.0-10.0 sec  3.32 GBytes  2.85 Gbits/sec
[SUM]  0.0-10.0 sec  6.63 GBytes  5.69 Gbits/sec

...full bandwith (5.66 Gbits/sec) in the opposite direction

(Test figures are from davem 4.0.0-rc5+, on 3.19.2 they were quite the same)

------------------------

Tried a look at differences in kernel .config
between the versions where the problem occured

diff /boot/config-3.16.0-0.bpo.4-amd64 /boot/config-3.19.0 | less

there is one occurence of TCP
'> # CONFIG_TCP_CONG_DCTCP is not set

but it should not hurt if it is not set, should it?

All the other stuff does not ring any bell wiht my (very limited) range of 
experience.


So what next?



Wolfgang Rosner

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