Return-path: Received: from mail-wg0-f50.google.com ([74.125.82.50]:37604 "EHLO mail-wg0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751613Ab3KTOvK (ORCPT ); Wed, 20 Nov 2013 09:51:10 -0500 Received: by mail-wg0-f50.google.com with SMTP id k14so9293685wgh.5 for ; Wed, 20 Nov 2013 06:51:09 -0800 (PST) Date: Wed, 20 Nov 2013 15:50:35 +0100 From: Karl Beldan To: Felix Fietkau Cc: Johannes Berg , linux-wireless Subject: Re: [PATCH] mac80211: use capped prob when computing throughputs Message-ID: <20131120145035.GB9335@magnum.frso.rivierawaves.com> (sfid-20131120_155114_123938_113FD4D5) References: <1384908668-27869-1-git-send-email-karl.beldan@gmail.com> <528C6590.1000803@openwrt.org> <20131120135628.GA9335@magnum.frso.rivierawaves.com> <528CC172.1040402@openwrt.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <528CC172.1040402@openwrt.org> Sender: linux-wireless-owner@vger.kernel.org List-ID: On Wed, Nov 20, 2013 at 03:04:34PM +0100, Felix Fietkau wrote: > On 2013-11-20 14:56, Karl Beldan wrote: > > On Wed, Nov 20, 2013 at 08:32:32AM +0100, Felix Fietkau wrote: > >> On 2013-11-20 01:51, Karl Beldan wrote: > >> > From: Karl Beldan > >> > > >> > Commit 3e8b1eb "mac80211/minstrel_ht: improve rate selection stability" > >> > introduced a local capped prob in minstrel_ht_calc_tp but omitted to use > >> > it to compute the rate throughput. > >> > > >> > Signed-off-by: Karl Beldan > >> > CC: Felix Fietkau > >> Nice catch! > >> Acked-by: Felix Fietkau > >> > > Interestingly enough, consecutive coding rates (5/6, 3/4, 2/3) max ratio > > is 9/10, did you do it on purpose ? (e.g. (9/10) * (5/6) == 3/4, > > (9/10) * (3/4) == 2/3 + 11/120). > The change has nothing to do with coding rates, it's only about > retransmissions caused by collisions under load. > I understand this, my point was that along with this comes the following: let's say my SNR is just not so good to get 5/6 as good as 3/4, and e.g. case1 htMCS7 has 91% htMCS6 has 100% success case2 htMCS7 has 80% htMCS6 has 100% success capping at 90% will prefer htMCS7 in case1 and htMCS6 in case2 both achieving best real throughput. capping at 80% will prefer htMCS7 in case1 _but_ htMCS7 in case2 the latter being the worst real throughput(90% of 5/6 == 100% of 3/4 > 80% of 5/6). Karl