[SOLVED] Slow Outbound Transmissions Over WiFi

[SDNick484]

EDIT 2 [SOLVED]: It took some digging, but I found out my issue -- I need to pass the parameter "11n_disable=8" to iwlwifi in order to enable AMPDU and get N level speeds. I think the name of the parameter and the value ought to be changed, but that's a kernel issue, not a Gentoo one. Anyways, I hope this helps someone else. More info here & here.

EDIT: I confirmed wired gigabit works fine, the issue is purely with WiFi.

I recently purchased a new laptop with the Intel Centrino Advanced-N 6205 WiFi (iwlwifi) card & Intel 82579LM Gigabit NIC (e1000e), and I've noticed my outbound transfer rate over WiFi is about a quarter of my inbound one. I first noticed this in scp, then have confirmed this in iperf. At this point, I'm not sure if it's a issue with the kernel module, TCP tunings, etc. However I seem to get the outbound transfer rate limit of around ~32Mbps (regardless of my distance to the AP) whereas inbound ranges from 80-140Mbps depending on proximity.

Below are some tests where:
server = On Wired Gigabit
laptop = On WiFi (5Ghz N)
(this is on a flat network with just 1 switch, a WNDR3700 running OpenWRT)

Outbound from laptop to server (~3 ft between laptop & access point):
<<<<<
nick@laptop ~ $ iperf3 -c server
Connecting to host lisa, port 5201
[ 4] local 192.168.1.112 port 39479 connected to 192.168.1.78 port 5201
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 3.90 MBytes 32.7 Mbits/sec 0 58.0 KBytes
[ 4] 1.00-2.00 sec 3.66 MBytes 30.7 Mbits/sec 0 66.5 KBytes
[ 4] 2.00-3.00 sec 3.11 MBytes 26.1 Mbits/sec 0 70.7 KBytes
[ 4] 3.00-4.00 sec 3.35 MBytes 28.1 Mbits/sec 0 70.7 KBytes
[ 4] 4.00-5.00 sec 3.48 MBytes 29.2 Mbits/sec 0 70.7 KBytes
[ 4] 5.00-6.00 sec 3.49 MBytes 29.2 Mbits/sec 0 90.5 KBytes
[ 4] 6.00-7.00 sec 3.58 MBytes 30.0 Mbits/sec 0 90.5 KBytes
[ 4] 7.00-8.00 sec 3.37 MBytes 28.2 Mbits/sec 0 90.5 KBytes
[ 4] 8.00-9.00 sec 3.70 MBytes 31.0 Mbits/sec 0 90.5 KBytes
[ 4] 9.00-10.00 sec 3.89 MBytes 32.6 Mbits/sec 0 90.5 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 35.5 MBytes 29.8 Mbits/sec 0 sender
[ 4] 0.00-10.00 sec 35.4 MBytes 29.7 Mbits/sec receiver

iperf Done.
>>>>>

Inbound to laptop from server (~3 ft between laptop & access point):
<<<<<<
nick@server ~ $ iperf3 -c laptop
Connecting to host laptop, port 5201
[ 4] local 192.168.1.78 port 50908 connected to 192.168.1.112 port 5201
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 16.6 MBytes 140 Mbits/sec 2 175 KBytes
[ 4] 1.00-2.00 sec 16.6 MBytes 140 Mbits/sec 0 198 KBytes
[ 4] 2.00-3.00 sec 16.7 MBytes 140 Mbits/sec 0 209 KBytes
[ 4] 3.00-4.00 sec 16.2 MBytes 136 Mbits/sec 0 215 KBytes
[ 4] 4.00-5.00 sec 16.2 MBytes 136 Mbits/sec 0 216 KBytes
[ 4] 5.00-6.00 sec 15.8 MBytes 132 Mbits/sec 26 167 KBytes
[ 4] 6.00-7.00 sec 16.5 MBytes 138 Mbits/sec 0 194 KBytes
[ 4] 7.00-8.00 sec 16.1 MBytes 135 Mbits/sec 0 209 KBytes
[ 4] 8.00-9.00 sec 14.9 MBytes 125 Mbits/sec 5 157 KBytes
[ 4] 9.00-10.00 sec 16.4 MBytes 137 Mbits/sec 0 173 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 162 MBytes 136 Mbits/sec 33 sender
[ 4] 0.00-10.00 sec 162 MBytes 136 Mbits/sec receiver

iperf Done.
>>>>>

Below is a scp test in both directons
<<<<<
nick@server ~ $ dd if=/dev/zero of=bigfile bs=1048576 count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.37431 s, 280 MB/s
nick@server ~ $ scp bigfile snowball:~/
bigfile 100% 100MB 11.1MB/s 12.3MB/s 00:09
nick@server ~ $ scp snowball:~/bigfile .
bigfile 100% 100MB 3.9MB/s 4.1MB/s 00:26
>>>>>


Any ideas on where I should start looking? I've already tried upping the rmem_max, wmem_max, etc. (as suggested here) to no avail.

[eccerr0r]

Thanks for the tip, I never really noticed any problems (sort of "happy it works") now I have to see if I'm also afflicted by this... I did notice my wifi was never anywhere close to theoretical speeds, blaming airwave noise by other peoples' APs and wifi devices...
_________________
Intel Core i7 2700K/Radeon R7 250/24GB DDR3/256GB SSD
What am I supposed watching?

[SDNick484]