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workarounds for very slow wifi using iwlagn driver?

asked 2011-11-23 15:36:53 -0600

alexlan gravatar image

Just upgraded to f16 and I get intermittent connection problems and very slow wireless speed even when I can connect. This hardware was and wifi was working fine in f14. I am using the iwlagn, lscpi reports that I have the Intel Centrino Advanced-N + WiMax 6250 (rev5f) chip:

$ lspci 
00:00.0 Host bridge: Intel Corporation Core Processor DRAM Controller (rev 02)
00:02.0 VGA compatible controller: Intel Corporation Core Processor Integrated Graphics Controller (rev 02)
00:16.0 Communication controller: Intel Corporation 5 Series/3400 Series Chipset  HECI Controller (rev 06)
00:19.0 Ethernet controller: Intel Corporation 82577LC Gigabit Network Connection (rev 06)
00:1a.0 USB Controller: Intel Corporation 5 Series/3400 Series Chipset USB2 Enhanced Host Controller (rev 06)
00:1b.0 Audio device: Intel Corporation 5 Series/3400 Series Chipset High Definition Audio (rev 06)
00:1c.0 PCI bridge: Intel Corporation 5 Series/3400 Series Chipset PCI Express Root Port 1 (rev 06)
00:1c.1 PCI bridge: Intel Corporation 5 Series/3400 Series Chipset PCI Express Root Port 2 (rev 06)
00:1c.2 PCI bridge: Intel Corporation 5 Series/3400 Series Chipset PCI Express Root Port 3 (rev 06)
00:1d.0 USB Controller: Intel Corporation 5 Series/3400 Series Chipset USB2 Enhanced Host Controller (rev 06)
00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev a6)
00:1f.0 ISA bridge: Intel Corporation Mobile 5 Series Chipset LPC Interface Controller (rev 06)
00:1f.2 SATA controller: Intel Corporation 5 Series/3400 Series Chipset 4 port SATA AHCI Controller (rev 06)
00:1f.6 Signal processing controller: Intel Corporation 5 Series/3400 Series Chipset Thermal Subsystem (rev 06)
01:00.0 SD Host controller: Ricoh Co Ltd MMC/SD Host Controller (rev 01)
02:00.0 Network controller: Intel Corporation Centrino Advanced-N + WiMAX 6250 (rev 5f)
ff:00.0 Host bridge: Intel Corporation Core Processor QuickPath Architecture Generic Non-core Registers (rev 02)
ff:00.1 Host bridge: Intel Corporation Core Processor QuickPath Architecture System Address Decoder (rev 02)
ff:02.0 Host bridge: Intel Corporation Core Processor QPI Link 0 (rev 02)
ff:02.1 Host bridge: Intel Corporation Core Processor QPI Physical 0 (rev 02)
ff:02.2 Host bridge: Intel Corporation Core Processor Reserved (rev 02)
ff:02.3 Host bridge: Intel Corporation Core Processor Reserved (rev 02)

I did some Googling and it seems there are problems with the driver in kernels > 2.3.40 (I'm on kernel-2.6.35.14-103.fc14.x86_64), but the kernel bug is about not being able to connect at all, whereas, I can connect, but it is very slow. This has also been reported on Fedora forum

Any known workarounds?

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answered 2011-11-23 17:17:13 -0600

alexlan gravatar image

updated 2011-11-23 17:23:44 -0600

I disabled n mode using:

modprobe -r iwlagn
modprobe iwlagn 11n_disable=1

as per Ubuntu forum post and performance is better. I noticed that iwconfig was showing many excessive retries:

wlan0     IEEE 802.11abgn  ESSID:"roosevelt"  
          Mode:Managed  Frequency:2.457 GHz  Access Point: 00:1C:DF:EF:02:ED   
          Bit Rate=104 Mb/s   Tx-Power=15 dBm   
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=63/70  Signal level=-47 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:21  Invalid misc:21   Missed beacon:0

with "n" disabled the number Tx excessive retries has dropped to zero (still get Invalid misc"):

wlan0     IEEE 802.11abg  ESSID:"roosevelt"  
          Mode:Managed  Frequency:2.457 GHz  Access Point: 00:1C:DF:EF:02:ED   
          Bit Rate=54 Mb/s   Tx-Power=15 dBm   
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=68/70  Signal level=-42 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:84   Missed beacon:0

See also this bugzilla issue in Fedora

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Asked: 2011-11-23 15:36:53 -0600

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Last updated: Nov 23 '11