Return-path: Received: from mail.candelatech.com ([208.74.158.172]:59834 "EHLO ns3.lanforge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754400Ab1BGSXX (ORCPT ); Mon, 7 Feb 2011 13:23:23 -0500 Message-ID: <4D503897.9040905@candelatech.com> Date: Mon, 07 Feb 2011 10:23:19 -0800 From: Ben Greear MIME-Version: 1.0 To: Felix Fietkau CC: "linux-wireless@vger.kernel.org" Subject: Re: Scanning and channel types. References: <4D4EF004.3040109@candelatech.com> <4D4EF99D.5020601@openwrt.org> <4D4EFC76.6090000@candelatech.com> <4D4EFD87.4010005@openwrt.org> In-Reply-To: <4D4EFD87.4010005@openwrt.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: On 02/06/2011 11:59 AM, Felix Fietkau wrote: > On 2011-02-06 8:54 PM, Ben Greear wrote: >> On 02/06/2011 11:42 AM, Felix Fietkau wrote: >>> On 2011-02-06 8:01 PM, Ben Greear wrote: >>>> Current code always sets the channel type to NO_HT when scanning. >>>> >>>> From what I can tell, we should be able to send NO_HT packets on >>>> any channel type, and for passive scanning, it should not matter >>>> at all what channel-type we are using. >>>> >>>> I tested relaxing scanning to use the current channel type >>>> when scanning on the operating channel, and it seems to >>>> work. >>>> >>>> Does anyone see any problems with this approach? >>> One thing you should make sure is that once you're done associating to >>> an NO_HT or HT20 AP (and you have no other interfaces to consider), the >>> channel mode must not be HT40 - otherwise it could reduce throughput. >> >> That is currently handled correctly by the ieee80211_set_channel_type >> method, as far as I can tell... >> >> Regardless of that, in my multi-vif testing, I see lower throughput when >> using HT40- than using HT20 (between 128 ath9k vif machine and 1 VAP ath9k machine). >> The VIFS all claim 300Mbps rate. >> I haven't looked into this any further at this point... > Well, with HT40 you take a hit from not just the busy time of the > primary channel, but also from the busy time of the extension channel. > If you have other wifi activity on the extension channel, then it's > normal that this would reduce throughput. I think you perfectly described the problem. I had another system that had a bunch of STAs configured and was making all sorts of noise. With it powered down, latency & throughput looks quite nice with 300Mbps HT40- (128 stas, 20kbps per sta tx and rx to other stas). Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com