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[SOLVED] Slow Outbound Transmissions Over WiFi
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SDNick484
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Joined: 05 Dec 2005
Posts: 212

PostPosted: Sat Nov 29, 2014 9:02 am    Post subject: [SOLVED] Slow Outbound Transmissions Over WiFi Reply with quote

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.
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eccerr0r
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Joined: 01 Jul 2004
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Location: almost Mile High in the USA

PostPosted: Sat Nov 29, 2014 9:57 pm    Post subject: Reply with quote

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...
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SDNick484
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Joined: 05 Dec 2005
Posts: 212

PostPosted: Sun Nov 30, 2014 8:13 pm    Post subject: Reply with quote

eccerr0r wrote:
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...


Yeah, now I'm curious about my "old" laptop. It looks like the commit, 205e2210daa975d92ace485a65a31ccc4077fe1a, went in around Feb., and I think hit the 3.11.x kernel range. It applies to a lot of Intel cards (pretty much anything that uses iwldvm) so I'm sure a lot of folks are affected and just are not aware. It's somewhat of an insideous change since it causes breakage that's suddle enough not to notice for quite some time and tha parameter related to it doesn't make much sence (personally, I'd expect 11n_disable to disable 11n...).
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