Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753262AbYKXKe3 (ORCPT ); Mon, 24 Nov 2008 05:34:29 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751939AbYKXKeS (ORCPT ); Mon, 24 Nov 2008 05:34:18 -0500 Received: from xc.sipsolutions.net ([83.246.72.84]:45028 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751000AbYKXKeQ (ORCPT ); Mon, 24 Nov 2008 05:34:16 -0500 Subject: Re: [ath5k-devel] Unusually low speeds with ath5k and iwl3945 From: Johannes Berg To: Felix Fietkau Cc: Benoit PAPILLAULT , Maxim Levitsky , Derek Smithies , ath5k-devel@venema.h4ckr.net, linux-wireless@vger.kernel.org, linux-kernel@vger.kernel.org, ipw3945-devel@lists.sourceforge.net, wally@theblackmoor.net In-Reply-To: <492A7733.2000205@openwrt.org> References: <492719ED.5000006@gmail.com> <20081122005240.GA27826@hash.localnet> <4927FC0C.10900@gmail.com> <492A5913.3070007@free.fr> <492A7733.2000205@openwrt.org> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-jL3RWv5L57vxZBEb5dgW" Date: Mon, 24 Nov 2008 11:34:06 +0100 Message-Id: <1227522846.3599.61.camel@johannes.berg> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3477 Lines: 81 --=-jL3RWv5L57vxZBEb5dgW Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Mon, 2008-11-24 at 10:43 +0100, Felix Fietkau wrote: > Benoit PAPILLAULT wrote: > > I did a similar test here and results is very strange. AP was my good > > old linksys WRT54G running an iperf server. Client was a laptop running > > either ath5k or madwifi/trunk and an iperf client. Channel is 5. Both > > drivers show the same behaviour. > >=20 > > At the beginning, throughput was very low : 500 - 600 kbit/s. Suddenly > > (after few minutes), it jumps to 15 - 17 Mbit/s and then few minutes > > later (let's say 10 - 20 minutes maybe), it jumps back to 500 - 600 > > kbit/s. Using a fixed rate has no effect. > >=20 > > I used my latest wireless monitoring tools and I did not saw lost of > > duplicates or lost packets. The only difference was the number of > > packets sent by seconds.... > >=20 > > Looking a my syslog, I just saw few messages, unrelated in time with th= e > > throughput going up or down. They were: > > - ath5k : unsupported jumbo > > - switching to short barker preamble > > - switching to long barker preamble > >=20 > > I can repeat the same test with iwl3945 as well, if needed. > While reading the code for calculating the frame duration, i noticed > something odd: It doesn't seem to be taking into account the short > vs long preamble distinction for ERP rates. IMHO this might be causing > issues like this. I've seen similar behaviour a long time ago when testin= g > iwl3945 against a Broadcom AP with exactly the same throughput drop (500- > 600 kbits/s). > When I analyzed the problem with an extra monitor mode card, I found out > that the throughput drop is caused by a huge number of retransmissions, > and if I remember correctly (I didn't look for this specifically back the= n), > the retransmissions went down the rate scaling table until they hit the > first non-ERP rate and that one worked on the first try. >=20 > Johannes, does that sound like a probable cause? If so, it should be easy > to fix. I have no idea. Shouldn't that be easy to tell from the monitor? And if the short/long switching was _unrelated_ in time it seems like it wouldn't be a problem? johannes --=-jL3RWv5L57vxZBEb5dgW Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Comment: Johannes Berg (powerbook) iQIcBAABAgAGBQJJKoMaAAoJEKVg1VMiehFYSGEQALOd9p4Y+Et73/WcDVfIhy92 SNYQdW90RXdaW1QIKaPVIWhU2uoy2EATx0enyZowPCIr66iX+Z4kzwMACmhKa2yz AsmujCDFCPzBy7W53ZUBDRnFjtGWOTu/t5YbxvP5lY5rAlXbTa24DP2LlFhAOj5A GDSeVm/QeRQGn6apugk3tKJt354HO55zl76Iuq5Mdqmu/s09dxRlbAT8bKYKNSms Qcfd8brnMtIdjCqteR7kkerF98rGcjpkn2g5U3MQSMzEKGdVIlwiYT8QSWVsn5H6 CFySyqiPYm5JfUnO+jMNF/xqYh3o2oDzqxYAv2+FsKJmQAVEhZF3xchWcWb6eyOF 27eSiTtvucCGEpkbWnzjDttLOOsji0UQgS1SsmqFeCarKwaJXQR75HlrzpIwgB8a 2u1BX8siVy6ne8p0PVJZ5MSmbgosMQeLPZmYttMb8NpwUFTkPOzu3ALf4QjamzjQ lPP4g+3TrXNj/v5SiUXHCPmyx1B8sJTGHZXJDtEPtSo41Jno9osNLnYeufMGwaGt 2rSdHpg6muM5kKWMdzF4y+mGLkLTwDL5ov3tXRtg4uRpPnHPY42C7KgTPrPWjP8N FYpxex0wF6mPFDgJPzcFxpruuHfWgqfzo6AR/2eWSUpxTx6buevDLCnNasV2zv60 L1LkhRCfGwR/1BNYGq4N =GqjT -----END PGP SIGNATURE----- --=-jL3RWv5L57vxZBEb5dgW-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/