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Message-ID: <0b6cf76d-e64d-4a35-b006-20946e67da6e@lunn.ch>
Date: Tue, 27 May 2025 14:51:29 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Ricard Bejarano <ricard@...arano.io>
Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>,
netdev@...r.kernel.org, michael.jamet@...el.com,
YehezkelShB@...il.com, andrew+netdev@...n.ch, davem@...emloft.net,
edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Subject: Re: Poor thunderbolt-net interface performance when bridged
> root@red:~# iperf3 -c 10.0.0.2 -u -b 1100M -t 5 # blue
> Connecting to host 10.0.0.2, port 5201
> [ 5] local 10.0.0.1 port 46140 connected to 10.0.0.2 port 5201
> [ ID] Interval Transfer Bitrate Total Datagrams
> [ 5] 0.00-1.00 sec 131 MBytes 1.10 Gbits/sec 94897
> [ 5] 1.00-2.00 sec 131 MBytes 1.10 Gbits/sec 94959
> [ 5] 2.00-3.00 sec 131 MBytes 1.10 Gbits/sec 94959
> [ 5] 3.00-4.00 sec 131 MBytes 1.10 Gbits/sec 94959
> [ 5] 4.00-5.00 sec 131 MBytes 1.10 Gbits/sec 94951
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams
> [ 5] 0.00-5.00 sec 656 MBytes 1.10 Gbits/sec 0.000 ms 0/474725 (0%) sender
> [ 5] 0.00-5.00 sec 597 MBytes 1.00 Gbits/sec 0.004 ms 42402/474725 (8.9%) receiver
> root@red:~#
>
> Here are the stat diffs for each interface:
>
> 1) red's br0 (10.0.0.1)
> RX: bytes packets errors dropped missed mcast
> +1055 +14 - - - -
> TX: bytes packets errors dropped carrier collsns
> +707341722 +474740 - - - -
>
> 2) red's tb0
> RX: bytes packets errors dropped missed mcast
> +1251 +14 - - - -
> TX: bytes packets errors dropped carrier collsns
> +707341722 +474740 - - - -
>
> 3) blue's tb0
> RX: bytes packets errors dropped missed mcast
> +707028822 +474530 +5 - - -
> TX: bytes packets errors dropped carrier collsns
> +1251 +14 - - - -
>
> 4) blue's br0 (10.0.0.2)
> RX: bytes packets errors dropped missed mcast
> +700385402 +474530 - - - -
> TX: bytes packets errors dropped carrier collsns
> +1251 +14 - - - -
>
> So, if I'm reading this right, loss happens at blue tb0 RX.
> We have 5 errors there and lost 210 packets.
>
> Also, why does iperf3 report 42402 lost packets, though?
210 lost is probably not enough to cause the TCP issue. The difference
between 210 and 42402 probably means the loss is happening higher up
the stack. But the majority are reaching blue, and then getting
dropped. So maybe look at IP and UDP statistics, are the packets
corrupt, failing CRC errors? netstat(1) and ss(1) will help you.
Another thing to try is run tcpdump on blue can capture some of the
packets to a file. Feed the file to wireshark. Unlike tcpdump,
wireshark checks all the CRCs and will tell you if they are wrong.
Andrew
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