Return-path: Received: from mrs.ro ([109.74.194.28]:50846 "EHLO mrs.ro" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751850AbbBVMVH (ORCPT ); Sun, 22 Feb 2015 07:21:07 -0500 Message-ID: <54E9C852.50809@mrs.ro> (sfid-20150222_132111_664352_169480CB) Date: Sun, 22 Feb 2015 14:15:14 +0200 From: Valentin Manea MIME-Version: 1.0 To: linux-wireless@vger.kernel.org CC: emmanuel.grumbach@intel.com, eran.harary@intel.com Subject: iwlwifi: ampdu_factor for iwl-6000 is set to 0 Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: 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. Regards, Valentin