Linux iwlwifi 801.11n speeds

Linux iwlwifi 801.11n speeds

[Thomas Fjellstrom]

Hi,

I've been doing some reasearch and testing lately, and have noticed that 
802.11n speeds in linux on two iwlwifi devices (6300, 6205) are anywhere from 
20 to 40mbps slower than in windows 7.

I've tried enabling swcrypto and disabling power management, and neither help.

While signal strength seems to be better in windows based on the signal meter, 
they may just calculate signal bars differently. I don't know.

Is there anything I can do to achieve similar speeds? I easily reach 90+ mbps 
in windows, and rarely reach 70 mbps in linux.

I'm running debian sid, with the 3.14.7 and 3.14.4 debian kernels, and should 
have the latest iwlwifi firmware.

I have a dual band Ubiquity AP Pro ap connected to a Sokeris 6501-50 firewall 
appliance running debian sid as well, and connected to a full GbE lan, which 
regularly achieves full speeds of 90MBps+. All settings on the actual network 
were not changed between speed tests. N was tested solely on the 5Ghz band, 
channel 36, and there is very little interference here on 5ghz. There is one 
other network visible and its on the other end of the 5ghz band.

Oh, and my nexus 7 (2013) also achieves 90mbps+, it may even get better, but I 
haven't managed to test local speeds, just tested with the speedtest.net app, 
and my internet is 100mbps, so it pretty much maxes it out.

Thank you for any assistance.

-- 
Thomas Fjellstrom
thomas@fjellstrom.ca

Re: Linux iwlwifi 801.11n speeds

[Peter Wu]

On Monday 30 June 2014 15:43:36 Thomas Fjellstrom wrote:
> Hi,
> 
> I've been doing some reasearch and testing lately, and have noticed that
> 802.11n speeds in linux on two iwlwifi devices (6300, 6205) are anywhere
> from 20 to 40mbps slower than in windows 7.
> 
> I've tried enabling swcrypto and disabling power management, and neither
> help.
> 
> While signal strength seems to be better in windows based on the signal
> meter, they may just calculate signal bars differently. I don't know.
> 
> Is there anything I can do to achieve similar speeds? I easily reach 90+
> mbps in windows, and rarely reach 70 mbps in linux.
> 
> I'm running debian sid, with the 3.14.7 and 3.14.4 debian kernels, and
> should have the latest iwlwifi firmware.
> 
> I have a dual band Ubiquity AP Pro ap connected to a Sokeris 6501-50
> firewall appliance running debian sid as well, and connected to a full GbE
> lan, which regularly achieves full speeds of 90MBps+. All settings on the
> actual network were not changed between speed tests. N was tested solely on
> the 5Ghz band, channel 36, and there is very little interference here on
> 5ghz. There is one other network visible and its on the other end of the
> 5ghz band.
> 
> Oh, and my nexus 7 (2013) also achieves 90mbps+, it may even get better, but
> I haven't managed to test local speeds, just tested with the speedtest.net
> app, and my internet is 100mbps, so it pretty much maxes it out.

Have you tried setting the module param 11n_disable=8?

I have this in my modprobe.conf:

# Enable AMPDU (otherwise there is a performance regression from 80
# Mbit/s to 20 Mbit/s). Introduced with v3.13-10103-g205e221 ("iwlwifi:
# disable TX AMPDU by default for iwldvm").
options iwlwifi 11n_disable=8

Kind regards,
Peter
https://lekensteyn.nl

Re: Linux iwlwifi 801.11n speeds

[Thomas Fjellstrom]

On Tue 01 Jul 2014 10:23:43 AM Peter Wu wrote:
> # Enable AMPDU (otherwise there is a performance regression from 80
> # Mbit/s to 20 Mbit/s). Introduced with v3.13-10103-g205e221 ("iwlwifi:
> # disable TX AMPDU by default for iwldvm").

Ah, that did it. Thank you! I didn't see that option (8) in my search. Lots of 
people disabling 802.11n completely, but that's kind of the opposite of what I 
want :)

Do you, or anyone else here know what the actual issue is with some cards that 
caused this change to be made? I saw one reference to a device reset happening 
occasionally. I can say I have not seen such crashes or resets. If I do, I'll 
report asap. Maybe it's related to various other settings hitting some odd 
corner case in the wifi firmware.

Question is, why is it enabled in windows if it causes so many problems that 
linux has to disable it by default? Do the windows drivers include fixed 
firmware? Or maybe a more complex quirks list? It'd be interesting to see what 
the two drivers do differently.

-- 
Thomas Fjellstrom
thomas@fjellstrom.ca