Hi, On Sun, 2015-02-22 at 14:15 +0200, Valentin Manea wrote: > Hi, > > Recently I started using kernel 3.19 from Ubuntu ppa and I noticed a > big drop in Wifi throughput. After some investigation I found that my > router was reporting the AMPDU factor changed from 3(in 3.18) to 0(in 3.19): > cat > /sys/kernel/debug/ieee80211/phy1/netdev:wlan1/stations/c4:xx:xx:xx:xx:xx/ht_capa: > ht supported > cap: 0x1066 > HT20/HT40 > Dynamic SM Power Save > RX HT20 SGI > RX HT40 SGI > No RX STBC > Max AMSDU length: 3839 bytes > DSSS/CCK HT40 > ampdu factor/density: 3/5 > MCS mask: ff ff 00 00 00 00 00 00 00 00 > MCS tx params: 1 > > ht supported > cap: 0x1066 > HT20/HT40 > Dynamic SM Power Save > RX HT20 SGI > RX HT40 SGI > No RX STBC > Max AMSDU length: 3839 bytes > DSSS/CCK HT40 > ampdu factor/density: 0/5 > MCS mask: ff ff 00 00 00 00 00 00 00 00 > MCS tx params: 1 > > In my setup this means a 50% drop in downstream throughput(from > 160Mbit/s to 80Mbit/s) > > I tracked down the offending commit and it seems this is it: > iwlwifi: change max HT and VHT A-MPDU exponent > c064ddf318aa51647a30108f7cd151c208c62eef > A new mechanism was created to have per device ampd_factor: > - ht_info->ampdu_factor = IEEE80211_HT_MAX_AMPDU_64K; > + ht_info->ampdu_factor = cfg->max_ht_ampdu_exponent; > > however the max_ht_ampdu_exponent is not set for any of the iwl-6000 > devices(including mine Intel Corporation Centrino Advanced-N 6235) > > #define IWL_DEVICE_6035 \ > .fw_name_pre = IWL6030_FW_PRE, \ > .ucode_api_max = IWL6035_UCODE_API_MAX, \ > .ucode_api_ok = IWL6035_UCODE_API_OK, \ > .ucode_api_min = IWL6035_UCODE_API_MIN, \ > .device_family = IWL_DEVICE_FAMILY_6030, \ > .max_inst_size = IWL60_RTC_INST_SIZE, \ > .max_data_size = IWL60_RTC_DATA_SIZE, \ > .nvm_ver = EEPROM_6030_EEPROM_VERSION, \ > .nvm_calib_ver = EEPROM_6030_TX_POWER_VERSION, \ > .base_params = &iwl6000_g2_base_params, \ > .eeprom_params = &iwl6000_eeprom_params, \ > .led_mode = IWL_LED_RF_STATE > > Since the original value of IEEE80211_HT_MAX_AMPDU_64K I would > suggest adding it to some iwl-6000 devices. > I did not submit any patches because I have no idea if there are > device which would not support this feature, however it worked before > with default value set to IEEE80211_HT_MAX_AMPDU_64K so I guess it must > be supported. >
Thank you for your report and analysis. You saved us a lot of time. I'll send a fix.
