Return-path: Received: from nbd.name ([46.4.11.11]:46872 "EHLO nbd.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752060Ab3KTPuF (ORCPT ); Wed, 20 Nov 2013 10:50:05 -0500 Message-ID: <528CDA23.9090303@openwrt.org> (sfid-20131120_165011_160009_B1107D6E) Date: Wed, 20 Nov 2013 16:49:55 +0100 From: Felix Fietkau MIME-Version: 1.0 To: Karl Beldan CC: Johannes Berg , linux-wireless Subject: Re: [PATCH] mac80211: use capped prob when computing throughputs 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> <20131120145035.GB9335@magnum.frso.rivierawaves.com> In-Reply-To: <20131120145035.GB9335@magnum.frso.rivierawaves.com> Content-Type: text/plain; charset=UTF-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 2013-11-20 15:50, Karl Beldan wrote: > 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). Not sure if that's a meaningful comparison at all - you're leaving out the per-packet overhead, which is important for the throughput calculation as well. - Felix