Horrible atheros wifi performance

[Rob Gom <rgom.debian@gmail.com>]

Hi all,
could you help me analyzing my wifi issue? I have atheros card and
internet access is very flaky, slow, unreliable, ping to wifi router
drops, things like that. When I connect my PC by external access
point, located in the same place and connected by ethernet to PC,
performance improves significantly.

Details:
- problem started appearing about 2.6.39, persists on 3.0
- I've found network articles about wifi performance on atheros in
2.6.38, which is supposedly fixed now on 2.6.38+
- I've tries compat wireless, but to no avail (no difference)
- I've tried disabling wifi card power management, but to no avail
- I've tried to add nohwcrypt to ath9k kernel module, but to no avail
- I've tried to switch to 2.6.38 for a while, but right after switch
to 2.6.38 and reboot to 2.6.39 performance was ok. I mean -
performance was ok for some minutes after reboot, then degraded after
probably power off-on cycle. In effect I have no conclusions from that
experiment.
- my home router is Linksys WRT54GC, not the best one, but causing no
problems for access point or some other machines (with broadcom wifi
cards)

I am not an wifi expert, so have no idea what to do next. I would
appreciate any suggestions.

[carramba@~]$ uname -a
Linux dom 3.0.0-1-686-pae #1 SMP Sun Jul 24 14:27:32 UTC 2011 i686 GNU/Linux

[carramba@~]$ lspci | grep Network
04:00.0 Network controller: Atheros Communications Inc. AR928X
Wireless Network Adapter (PCI-Express) (rev 01)

[carramba@~]$ sudo iwconfig wlan1
[sudo] password for carramba:
wlan1     IEEE 802.11bgn  ESSID:off/any
          Mode:Managed  Frequency:2.422 GHz  Access Point: Not-Associated
          Tx-Power=17 dBm
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
# currently using eth

[carramba@~]$ lsmod | grep ath
ath9k                  67270  0
mac80211              165768  1 ath9k
ath9k_common           12610  1 ath9k
ath9k_hw              250420  2 ath9k,ath9k_common
ath                    17181  2 ath9k,ath9k_hw
cfg80211              112970  3 ath9k,mac80211,ath


I've found no Debian bugs on that, only similar RedHat bug:
https://bugzilla.redhat.com/show_bug.cgi?id=700973 (other bugs
referred to 2.6.38 regression, mentioned above).

Home network structure:
PC with atheros card ------- Linksys WRT54GC router ------ internet
or
PC ethernet ------- TP Linkx WA500 or similar ------ Linksys WRT54GC
router ------ internet

Best regards,
Robert