[PATCH net v3 0/2] Fix TCP retransmissions on NS/NSP SoCs
From: Florian Fainelli
Date: Mon Oct 26 2026 - 17:07:25 EST
On Northstar and Northstar Plus SoCs we would see about 1000 TCP
retransmissions per second due to a rate mismatch between bgmac and b53,
make sure that we run at the same speed on both side to avoid dropping
packets on the floor.
This issue was found during testing on a Northstar Plus reference board
(BCM958625HR) while running iperf3 to a test machine and noticing
retranmsisions:
# iperf3 -c 192.168.3.1
Connecting to host 192.168.3.1, port 5201
[ 4] local 192.168.3.204 port 49856 connected to 192.168.3.1 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 4] 0.00-1.00 sec 111 MBytes 933 Mbits/sec 915 99.0 KBytes
[ 4] 1.00-2.00 sec 111 MBytes 928 Mbits/sec 909 109 KBytes
[ 4] 2.00-3.00 sec 110 MBytes 925 Mbits/sec 1097 99.0 KBytes
[ 4] 3.00-4.00 sec 111 MBytes 928 Mbits/sec 814 58.0 KBytes
[ 4] 4.00-5.00 sec 111 MBytes 930 Mbits/sec 1187 109 KBytes
[ 4] 5.00-6.00 sec 110 MBytes 923 Mbits/sec 893 72.1 KBytes
[ 4] 6.00-7.00 sec 111 MBytes 929 Mbits/sec 843 67.9 KBytes
[ 4] 7.00-8.00 sec 111 MBytes 928 Mbits/sec 920 79.2 KBytes
[ 4] 8.00-9.00 sec 111 MBytes 929 Mbits/sec 1109 66.5 KBytes
[ 4] 9.00-10.00 sec 111 MBytes 930 Mbits/sec 1055 63.6 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 4] 0.00-10.00 sec 1.09 GBytes 933 Mbits/sec 9742
sender
[ 4] 0.00-10.01 sec 1.09 GBytes 933 Mbits/sec
receiver
Changes in v3:
- correct commend in the second patch about what is being forced
on the CPU port, it's not just flow control, it's also speed
Changes in v2:
- make it apply cleanly to net/main
Florian Fainelli (2):
net: ethernet: bgmac: preserve forced 2.5 Gbps link speed
net: dsa: b53: restore the NSP IMP port 2 Gbps mode
drivers/net/dsa/b53/b53_common.c | 12 +++++++++---
drivers/net/ethernet/broadcom/bgmac.c | 8 ++++++--
2 files changed, 15 insertions(+), 5 deletions(-)
--
2.53.0