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Network throughput limited to ~530 Mbit/s on sw0p interfaces (expected gigabit) #69

@AcSully

Description

@AcSully

Environment:

Hardware platform: Custom board with STM32MP257DAK3

Buildroot version: 2025.02.5

External tree version: custom

Linux kernel version: 6.6.78

Defconfig used: custom

Network PHY: YT8531

Problem Description
When performing an iperf3 TCP test between a PC and the sw0p2 interface, the measured throughput is only about 530 Mbit/s, far below the expected ~940 Mbit/s for a gigabit link

Problem Description
When performing an iperf3 TCP test between a PC and the sw0p2 interface, the measured throughput is only about 530 Mbit/s, far below the expected ~940 Mbit/s for a gigabit link.

Steps to Reproduce

Boot the device and log in.

Run the switch startup script:

/usr/bin/switch_startup.sh
Assign IP addresses to the interfaces:

ifconfig sw0ep 192.168.10.181 up
ifconfig sw0p2 192.168.10.182 up
On the PC, set IP address 192.168.10.183.

From the device, run iperf3 as client to the PC server:

iperf3 -c 192.168.10.183
Actual Result

Connecting to host 192.168.10.183, port 5201
[ 5] local 192.168.10.181 port 34300 connected to 192.168.10.183 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 63.2 MBytes 530 Mbits/sec 1 154 KBytes
[ 5] 1.00-2.00 sec 62.8 MBytes 526 Mbits/sec 0 154 KBytes
[ 5] 2.00-3.00 sec 63.4 MBytes 532 Mbits/sec 0 154 KBytes
[ 5] 3.00-4.00 sec 62.6 MBytes 526 Mbits/sec 1 154 KBytes
[ 5] 4.00-5.00 sec 57.4 MBytes 481 Mbits/sec 0 154 KBytes
[ 5] 5.00-6.00 sec 63.0 MBytes 529 Mbits/sec 0 154 KBytes
[ 5] 6.00-7.00 sec 62.2 MBytes 522 Mbits/sec 0 154 KBytes
[ 5] 7.00-8.00 sec 61.6 MBytes 517 Mbits/sec 0 154 KBytes
[ 5] 8.00-9.00 sec 61.9 MBytes 519 Mbits/sec 0 154 KBytes
[ 5] 9.00-10.03 sec 63.5 MBytes 519 Mbits/sec 0 154 KBytes


[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.03 sec 634 MBytes 530 Mbits/sec 2 sender
[ 5] 0.00-10.03 sec 634 MBytes 530 Mbits/sec receiver

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