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I'm having a severe TCP receive problem with a new Ubuntu 16 server and
an Intel 82599ES 10-Gigabit SFP+ (X520 series card) when a windows 10
machine is used to send the data. The receive performance is 1Gb to 2Gb
steady using iperf single stream, while send is 9.42Gb.
Here is what I have found:
-Running 8 parallel streams in iperf gets me the full 9.42 in aggregate
-Tried a few windows 10 machines with repeatable same results
-Same results through switch or direct
-Linux to linux no problems
-Tested with clean installs of 16.04.02 and 4.4.0-66 kernel, latest the
upgrade will give me, also tried 17.04 with up to 4.10.0-20-generic same
problem, tried 4.11.0-041100rc8-generic and problem seemed to go away
for a bit but came back so I think that might be a red herring (see
interesting note below).
-14.04 and 15.10 with up to 4.2.8-040208-generic is 9.42/9.42 (works
fine, couldn't get 4.3 to install on 15.10)
-14.04 with the latest 5.0.4 ixgbe driver still works fine, does not
seem to be a driver version issue.
-Tried swapping out cards with another same model/chipset with same
exact result
-Large receive offload increases the performance from a steady 1Gb to a
steady 2.14Gb
-Disabling sack under got me 75% of the way back to full speed, but it
was very unstable (didn't hold at a solid speed)
-Using a different brand of card in this same server (but not the same
slot) (mellanox infiniband running in ethernet mode) is 9.42/8.5 (seems
to work fine, 9.42 to 8.5 is windows machine limit I think)
-Interesting: When swapping between intel and mellanox 10Gbe cards (with
a reboot of the server inbetween, but not a reboot of the windows
machine, and keeping the same IP on the server) the performance does not
change immediately. When going from intel to mellanox the first test
holds around 1 or 2Gbit, then after that it jumps up to 8.5 steady.
Similarly when switching from mellanox to Intel the first 1 or 2 seconds
of performance hits 8.x then drop in half or more and within 3 or 4
seconds it is back to 1Gbit and stays there for each subsequent iperf
test.
-Interesting: When capturing packets on wireshark on windows,
performance comes up to 8.5! (No, ditching windows isn't an option here
unfortunately. :) So obviously something in the way the two tcp stacks
are interacting without a buffer inbetween when the intel driver is
online is causing issues.
-Port bonding makes no difference (nor should it for single stream)
-Tried rolling the intel driver back to the 3.2.1 version that is on
14.04 but it was too old to compile
-I suspect this is a kernel TCP/IP implementation change somewhere
between 4.2 and 4.4 that has caused it to not play nice with window's
stack. Based on the delayed performance change I'm thinking something
is messing with flow control, the tcp congestion algorithm, or the tcp
window. I tried turning some various tcp options off, tweaking some
values, changing congestion algorithms, hardware flow control, and
comparing sysctl stuff from the u14 machine to this machine to no avail.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: bot-comment
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TCP/IP Throughput Limitation
https://bugs.launchpad.net/bugs/1698454
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