From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from xc.sipsolutions.net ([83.246.72.84]:37217 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751629AbZG2HTy (ORCPT ); Wed, 29 Jul 2009 03:19:54 -0400 Subject: Re: 31-rc3-mmotm0716 - wonky wireless statistics.. From: Johannes Berg To: Zhu Yi Cc: "Valdis.Kletnieks@vt.edu" , Andrew Morton , "linux-kernel@vger.kernel.org" , "linux-wireless@vger.kernel.org" In-Reply-To: <1248831078.3747.1117.camel@debian> References: <5934.1248814870@turing-police.cc.vt.edu> <1248831078.3747.1117.camel@debian> Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-f4FY58J+oUxAJBL7zAfQ" Date: Wed, 29 Jul 2009 09:19:12 +0200 Message-Id: <1248851953.13742.12.camel@johannes.local> Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: --=-f4FY58J+oUxAJBL7zAfQ Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Wed, 2009-07-29 at 09:31 +0800, Zhu Yi wrote: > > # cat /proc/net/wireless > > Inter-| sta-| Quality | Discarded packets | Mi= ssed | WE > > face | tus | link level noise | nwid crypt frag retry misc | be= acon | 22 > > wlan0: 0000 63. -47. -256 0 0 0 0 0 = 0 > > wlan1: 0000 0 0 0 0 0 0 0 0 = 0 > > wlan2: 0000 0 0 0 0 0 0 0 0 = 0 > >=20 > > Where did that -256 for "noise" come from? It ends up confusing the > > gkrellm-wifi plugin, it reports a S/N of 219dB ;) >=20 > This should be related to http://git.kernel.org/?p=3Dlinux/kernel/git/lin= ville/wireless-testing.git;a=3Dcommit;h=3Dfdb897ea5c77836f890033d563336ab0c= 94c9222 >=20 > But I don't think this is an ABI broken. User space should parse the > trailing '.' to see if a field is updated or not because there are cards > not capable to report hardware noise level anyway. Johannes? So I had to look at the code to figure out wtf is going on. Then the value shown is calculated as: ((__s32) stats->qual.noise) - ((stats->qual.updated & IW_QUAL_DBM) ? 0x100= : 0) and since we have dBm for the signal strength (and dBm is "all or nothing") you get -256 since we don't fill noise right now. However, it goes on like this: stats->qual.updated & IW_QUAL_NOISE_UPDATED ? '.' : ' ' so you're right -- the tool shouldn't be using the value unless followed by a dot ("."). Thus, your analysis is correct as far as I can tell -- it's a userspace bug and your userspace just happened to work correctly with this card, but would have been broken with almost all other wireless cards. johannes --=-f4FY58J+oUxAJBL7zAfQ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- iQIcBAABAgAGBQJKb/ftAAoJEODzc/N7+QmaXHEQAKCZi1mLwi6gkqCj+OqCw6dX jdYNfDRDi3+GSoSmjZgfg1/P/EC/XtsDj+F5ijLjHfj4uk8OqJqlteWfllbcfH9X TGjEGZizUlsQPXuFHLHa0MIWNvakzweGfiST5CxdOFSbiaPxQ1xWwsi8ky6QFNoI n1iNdF4ZJK6f2nQU0jv9jHeTdZPL5y1RcxXf7YaWoFw6lzMP1ke8FXIlr6c9BEMK aaM+OSzpTo+Lm2+k+PB8Ey2KOxrakcBcPtvqWQGP+PnOxNVs71ra2kScjFQCkdqY e3ZidN21rNg5G3tP/iCPSma4reRLwPFhXA95cFdfllBUFdnIdvzqopuGo5aBct8O b0ooe8Lwg8fghKGxq13FF33cDAsBLXsbes/t9zTZDh7r40U8OlfvoSSmPfZJ/qEP E6zdTiAgpCBL/nfjHvCZA/LPgqqT3MeGDCv095SdHwtGamt/jKqyPJWMRpU34mzb ESgd641IH9qd4sSBtzFi1AmuJzoHFzBzCCHUDQwEKwYArUTrUU368mpYlYRqpbHa IvBFofAeOxfNRfRkUy9YB/JczOeE3cx8PrCH+iHSLh8XGm5AmxI2pDHwqivrJh3z E2Wqmv76AP6TThJ8RJTi1/rGoIjHrkVqNerr+IISDXzqXhOFcWJCLGprZl0EIfwW w7R8A5fJkFEt/8IhRcY3 =DD4g -----END PGP SIGNATURE----- --=-f4FY58J+oUxAJBL7zAfQ--