[FS#891] Slow download speed over Ethernet (wpj344, QCA8334)

[LEDE Bugs]

The following task has a new comment added:

FS#891 - Slow download speed over Ethernet (wpj344, QCA8334)
User who did this - eripek (eripek)

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Some observation here:
4x TP-LINK TL-WR1043v2
1x TP-LINK TL-WDR3600
They are all QCA 8327, not 8334.

The TP-Links are all running LEDE 17.01.4 in a VLAN only setup. They are all connected with their blue WAN-Port, which is configured as a trunk port, to a Gigabit Ethernet Switch (various manufacturers)

Running iperf -c against a machine running Linux - 125-200 Mbit/s.
Running iperf -s / iperf -c between machines running Linux over three of the VLAN-aware Switches results in > 950 Mbit/s.
Running iperf between to 1043NDv2 connected by one the VLAN-aware switches results in in 90-166 Mbit/s. The same happens in between any of the TP-Link TL-W*s.
It seems to be the bottleneck for WLAN (Multi-SSID/VAP only) as well. All WLANs are limited to around 20-30 Mbit/s.

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More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=891#comment4665