Return-path: Received: from nbd.name ([46.4.11.11]:36922 "EHLO nbd.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755171Ab2J3NYY (ORCPT ); Tue, 30 Oct 2012 09:24:24 -0400 Message-ID: <508FD505.4080404@openwrt.org> (sfid-20121030_142428_008693_07D415D6) Date: Tue, 30 Oct 2012 14:24:21 +0100 From: Felix Fietkau MIME-Version: 1.0 To: Mathias Kretschmer CC: Simon Wunderlich , linux-wireless@vger.kernel.org, ath9k-devel@venema.h4ckr.net, linville@tuxdriver.com, mcgrof@qca.qualcomm.com, sven@narfation.org, Simon Wunderlich Subject: Re: [PATCH] ath9k: apply coverage class on slottime too References: <1351598855-21427-1-git-send-email-siwu@hrz.tu-chemnitz.de> <508FCB77.9000303@openwrt.org> <508FCF5A.2080204@fokus.fraunhofer.de> In-Reply-To: <508FCF5A.2080204@fokus.fraunhofer.de> Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 2012-10-30 2:00 PM, Mathias Kretschmer wrote: > On 10/30/2012 01:43 PM, Felix Fietkau wrote: >> On 2012-10-30 1:07 PM, Simon Wunderlich wrote: >>> From: Mathias Kretschmer >>> >>> According to 802.11-2007 17.3.8.6 (slot time), the slot time should >>> be increased by 3 us * coverage class. The code only increased the >>> ack timeout, which is fixed by this patch. >>> >>> We have noticed in our long shot scenario that we see less collisions >>> with this patch. >> At some point I had the slot time increase in the driver, but noticed a >> massive throughput degradation on 10-20 km links. Leaving the slot time >> alone and changing only the ACK timeout fixed this. What distances did >> you test? > > about 11km. did you test UDP (unidirectional) or TCP (bidirectional) throughput ? I always use TCP, because UDP tests are too unrealistic to estimate real performance. > The larger slot time will increase the channel access overhead which should impact > unidirectional throughput. > > With bidirectional traffic, the larger slottime should help to minimize collisions > on loaded links. Overall this seems to increase the net throughput for us, > especially in higher access categories (smaller backoff windows). When I ran the test, the throughput degradation was so big that the links became almost useless. It was a long time ago, so maybe this was caused by another bug that has been fixed since. I will run another test with this patch in a current version... - Felix