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Old 06-12-2013, 07:05 PM   #1
Registered: Feb 2010
Location: SD Bay Area
Posts: 270

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Lightbulb iwlwifi 802.11n usability resolved

Much net flotsam re: disappointing 801.11n performance from intel's Centrino-N series wireless controllers, including the backports.

After upgrading from 1337 to 14 (new 3.2.45 kernel) and a bit of module parameter tweaking, 11n is very acceptable compared to the 1337 iwlagn driver:
- no suspend/resume hangs or frequent disconnects
- great interactive performance
- 10MB/s (Bytes, not bits) throughput on a wireless -> 100bT LAN client rsync of Slackware 14 installation bits (about 1300MB)
- typical Bit Rates in the 180-270Mb/s range

Still get Tx retries but usability is no longer the issue. The router is an e2100L running dd-wrt build 21676:
- 40MHz channel width
- NG-Mixed
- channel 11, lower extension
- short preamble
- RTS/CTS enabled
~$ sudo lspci -v  -s 02:00
02:00.0 Network controller: Intel Corporation Centrino Advanced-N 6200 (rev 35)
	Subsystem: Intel Corporation Centrino Advanced-N 6200 2x2 AGN
	Flags: bus master, fast devsel, latency 0, IRQ 43
	Memory at da100000 (64-bit, non-prefetchable) [size=8K]
	Capabilities: [c8] Power Management version 3
	Capabilities: [d0] MSI: Enable+ Count=1/1 Maskable- 64bit+
	Capabilities: [e0] Express Endpoint, MSI 00
	Capabilities: [100] Advanced Error Reporting
	Capabilities: [140] Device Serial Number 00-23-14-ff-ff-0e-fe-2c
	Kernel driver in use: iwlwifi
~$ iwconfig wlan0
wlan0     IEEE 802.11abgn  ESSID:"2WIRE962"  
          Mode:Managed  Frequency:2.462 GHz  Access Point: 68:7F:74:C7:F7:63   
          Bit Rate=270 Mb/s   Tx-Power=15 dBm   
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=69/70  Signal level=-41 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:976381  Invalid misc:41   Missed beacon:0
options iwlwifi auto_agg=0 power_save=1 power_level=3 bt_coex_active=0
Here's the script used to monitor tweaking:
#!/bin/awk -f

# script to monitor TX aggregation issues with iwlwifi or iwlagn
# use: sudo tail -f -n 1000 /var/log/messages | <this awk script>
# edit 'wlan0' if it is not your wireless device
# edit 'iwlwifi' if you are using iwlagn
# prints running average of 'Tx aggregation enabled' errors per minute

/Linux version /{ print };
/iwlwifi .* Radio/{					# EDIT #
	sub("\\[",""); sub("]","");
	told=$6; tag=$0; R1=1
/wlan0: leased/{ print };				# EDIT #

R1==1 && /Tx agg/{
	R1=0; L1=1

L1==1 && /Tx agg/{
	sub("\\[",""); sub("]","");
	tnew=$6; tdelta=(tnew-told); told=tnew;
	tot+=tdelta; cnt++; avg=tot/cnt;

	printf "%s avg=%4.1f tot=%6.1f TX agg\n",

	if((cnt % 10)==0){
		system("iwconfig wlan0")		# EDIT #

L1==1 && /wlan0: carrier/{				# EDIT #
	print; L1=0; tdelta=tot=cnt=told=0

Last edited by lazardo; 06-13-2013 at 01:41 PM. Reason: tags ate my quotes, script corrected


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