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- 2022-09-15 krowe: Even with rx-gro-hw=off on naasc-vs-4, I am still seeing some retransmissions in iper3 tests. These are the same as TCP Retransmissions seen previously. On a modern, well-designed network I would expect to see almost no TCP Retransmissions. So this may indicate that there are still improvements to be made. The number of retransmissions seems to vary over time from 0 retransmissions to over a thousand retransmissions on certain directions. This makes me think there is something else using the 10Gb network that is interfering with my tests.
This is a 10 second iper3 test using TCP from the host in the left column to the host in the top row.
TableXX iperf3 Retransmissions over 10Gb and rx-gro-hw=off naasc-vs-2
(10.2.120.107)
naasc-vs-3
(10.2.120.109)
naasc-vs-4
(10.2.120.110)
naasc-vs-5
(10.2.120.112)
naasc-vs-2 0, 0, 0 0, 0, 0 45, 52, 59 naasc-vs-3 87, 0, 19, 1734 0, 0, 0 74, 52, 56 naasc-vs-4 0, 342, 1147, 363 0, 0, 0 83, 51, 50 naasc-vs-5 494, 0, 1296, 24 0, 0, 0 0, 0, 0 This looks like some sort of misconfiguration on the receiving ends of naasc-vs-2 and naasc-vs-5. This may be congestion. For example if I start an iper3 test from naasc-vs-4 to naasc-vs-2 I can often see 0 retransmissions every second. But then while doing that I also start in iper3 test from na-arc-1 (a guest on naasc-vs-4) to na-arc-6 (a guest on naasc-vs-2), I can see around 20 to 70 retransmissions per second on both naasc-vs-4 and na-arc-1. They are clearly interfering with each other. I don't see congestion when I reverse the test (naasc-vs-2 to naasc-vs-4 while na-arc-6 to na-arc-1). Doing the same test from naasc-vs-5 to naasc-vs-3 while doing na-arc-5 (a guest on naasc-vs-5) to na-arc-3 (a guest on naasc-vs-3) I don't see any congestion. If I turn off TSO on naasc-vs-2 with ethtool -K ens1f0np0 tx-tcp-segmentation off I then no longer can create congestion by doing two simultaneous iperf3 tests but I still get occational retransmissions (like 100+ per second) when testing from naasc-vs-{3..5} to naasc-vs-2. Disabling TSO also doesn't seem to reduce the number of retransmissions when testing from na-arc-* to na-arc-6.
TableXX iperf3 Retransmissions over 10Gb and rx-gro-hw=off na-arc-1
10.2.97.71
(naasc-vs-4)
na-arc-2
10.2.97.72
(naasc-vs-4)
na-arc-3
10.2.97.73
(naasc-vs-3)
na-arc-4
10.2.97.74
(naasc-vs-4)
na-arc-5
10.2.97.75
(naasc-vs-5)
na-arc-6
10.2.97.76
(naasc-vs-2)
na-arc-1 0, 0, 0 0, 0, 0 0, 0, 0 55, 75, 50 323, 501, 538 na-arc-2 0, 0, 0 0, 0, 0 0, 0, 0 68, 81, 64 768, 1050, 658 na-arc-3 1692, 1627, 2071 0, 1326, 592 1471, 3376, 686 360, 2477, 664 1873, 1872, 2384 na-arc-4 0, 0, 0 0, 0, 0 0, 0, 0 58, 86, 65 4, 9, 38 na-arc-5 108, 6, 6 6, 6, 6 2, 1, 1 6, 6, 6 1293, 1197, 33 na-arc-6 106, 0, 28 0, 0, 21 0, 88, 0 7, 0, 28 89, 75, 52 - I see a lot of dropped packets on the Rx side of all the naasc-vs hosts.
- I think the large number of retransmissions when transmissing from naasc-vs-* to naasc-vs-2 the cause for the large number of retransmissions when transmitting from na-arc-* to na-arc-6.
- I don't know what explains the retransmissions when transmitting from na-arc-3 to na-arc-*.
I don't think the retransmissions from na-arc-3 to na-arc-* can be atributed to MTU. Sure eth0 on na-arc-3 is 1500 while all the other na-arc nodes are 9000 but that should not cause a problem. If anything it sould be a problem the other way around. Also I tested changing na-arc-6 to 1500 and retransmissions didn't change. The lack of retransmissions between na-arc-1, na-arc-2, and na-arc-4 is because they are all on the same VM Host (naasc-vs-4).
- You can use ping to see if your packet size actually gets through. This is a good way to test MTU sizes.
ping -c 3 -M do -s 1500 na-arc-1
- You can use ping to see if your packet size actually gets through. This is a good way to test MTU sizes.
- Try increasing Rx buffers (ethtool -G) and see if that helps retransmits
- ethtool -G ens1f0np0 rx 4096
- ethtool -G ens1f0np0 tx 2048
- Setting these didn't seem to help with the TCP Retransmissions.
- ethtool -G ens1f0np0 rx 4096
- Map the retransmissions. Is there a pattern over time? A regular cadence?
- map background traffic
- Is the fact that APIPA (zeroconf) is configured an indication that some network device was not brought up properly
- What about ethtool -K ens1f0np0 tx-tcp-segmentation off
- What about net.core.netdev_budget
- https://access.redhat.com/articles/1391433
- dropwatch
Dropped packets
I see dropped Rx packets on interface ens1f0np0 on naasc-vs-2. About 1 or 2 packets per second. You can see this with watch ifconfig ens1f0np0. This is especially interesting given that there isn't much traffic on naasc-vs-2 right now. It is only hosting one VM guest (na-arc-6) and that guest is only running the docker agent container. I am not seeing any dropped packets on na-arc-6.
- 2022-09-26 krowe: ethtool -G ens1f0np0 tx 2048 and ethtool -G ens1f0np0 rx 4096 made no difference.
- 2022-09-26 krowe: ethtool -K ens1f0np0 tx-tcp-segmentation off made no difference
I see dropped Rx packets on all the other naasc-vs hosts as well but at a much slower rate.
Comparisons
naasc-vs-2, 3, 4, 5
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