[FS#1527] AR8327 low throughput

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - eripek (eripek) 

Attached to Project - OpenWrt/LEDE Project
Summary - AR8327 low throughput
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - mittel
Priority - gering
Reported Version - All
Due in Version - Undecided
Due Date - Undecided
Details - Affected devices and versions of LEDE/OpenWRT:
1x TL-WR1043NDv2 - OpenWrt SNAPSHOT, r6800-52ba576
3x TL-WR1043NDv2 - LEDE 17.01.4 (stable)
1x TL-WDR3600 - LEDE 17.01.4 (stable)

All of the above devices use AR8327 rev as their switch:
[    0.881815] switch0: Atheros AR8327 rev. 4 switch registered on ag71xx-mdio.0

Steps to reproduce:
A) iperf clients
3x TL-WR1043NDv2 connected by their WAN port, that is configured to act as vlan trunk port only.
1x TL-WDR3600 connected by it's WAN port, that is configured to act as vlan trunk port only.
1x TL-WR1043NDv2 connected by it's port no 4, that is configured to act as vlan trunk port only.
B) iperf server 1 (192.168.0.1)
C) iperf server 2 (192.168.0.11)
D) four gigabit ethernet easysmart/websmart switches with 1,5GB+ throughput, each, in between A,B,C.

1. Any A against B over cable - as an example:
Client connecting to 192.168.0.1, TCP port 5001
TCP window size: 43.8 KByte (default)
------------------------------------------------------------
[  3] local 192.168.0.75 port 35102 connected with 192.168.0.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   179 MBytes   150 Mbits/sec


2. C against B over each of the 4 devices in D:
Client connecting to 192.168.0.1, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[  3] local 192.168.0.11 port 56228 connected with 192.168.0.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.09 GBytes   938 Mbits/sec

Each of the TP-Links is using switch-only, no WAN, no NAT, but INPUT-iptables for their respective vlans, so another test of one of the A-devices against B w/o iptables:
------------------------------------------------------------
Client connecting to 192.168.0.1, TCP port 5001
TCP window size: 43.8 KByte (default)
------------------------------------------------------------
[  3] local 192.168.0.242 port 45976 connected with 192.168.0.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   213 MBytes   179 Mbits/sec

It seems, that devices containing AR8327 rev4 wont achieve more than 1/5 of the specified nominal LAN speeds, when acting as an endpoint.

Further observations: WLAN clients won't exceed 25-30 Mbit/s, when using one of the trunked vlans. (WLAN client iwlwifi, Centrino N 2230, e.g. in either 40 or 20 MHz against A-devices in 802.11n WDS AP mode).

Since this is no WAN to LAN scenario, (missing) HWNAT cannot be involved.
Why is the switch performance below expectations? Is this a hw issue or a driver problem?



More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1527