From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: Wrong network usage reported by /proc Date: Mon, 04 May 2009 19:53:54 +0200 Message-ID: <49FF2BB2.4030700@cosmosbay.com> References: <20090504171408.3e13822c@python3.es.egwn.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-kernel@vger.kernel.org, Linux Netdev List To: Matthias Saou Return-path: Received: from gw1.cosmosbay.com ([212.99.114.194]:39713 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753379AbZEDRyA convert rfc822-to-8bit (ORCPT ); Mon, 4 May 2009 13:54:00 -0400 In-Reply-To: <20090504171408.3e13822c@python3.es.egwn.lan> Sender: netdev-owner@vger.kernel.org List-ID: Matthias Saou a =E9crit : > Hi, >=20 > I'm posting here as a last resort. I've got lots of heavily used RHEL= 5 > servers (2.6.18 based) that are reporting all sorts of impossible > network usage values through /proc, leading to unrealistic snmp/cacti > graphs where the outgoing bandwidth used it higher than the physical > interface's maximum speed. >=20 > For some details and a test script which compares values from /proc > with values from tcpdump : > https://bugzilla.redhat.com/show_bug.cgi?id=3D489541 >=20 > The values collected using tcpdump always seem realistic and match th= e > values seen on the remote network equipments. So my obvious conclusio= n > (but possibly wrong given my limited knowledge) is that something is > wrong in the kernel, since it's the one exposing the /proc interface. >=20 > I've reproduced what seems to be the same problem on recent kernels, > including the 2.6.27.21-170.2.56.fc10.x86_64 I'm running right now. T= he > simple python script available here allows to see it quite easily : > https://www.redhat.com/archives/rhelv5-list/2009-February/msg00166.ht= ml >=20 > * I run the script on my Workstation, I have an FTP server enabled > * I download a DVD ISO from a remote workstation : The values match > * I start ping floods from remote workstations : The values reported > by /proc are much higher than the ones reported by tcpdump. I used > "ping -s 500 -f myworkstation" from two remote workstations >=20 > If there's anything flawed in my debugging, I'd love to have someone > point it out to me. TIA to anyone willing to have a look. >=20 > Matthias >=20 I could not reproduce this here... what kind of NIC are you using on affected systems ? Some ethernet drivers report stats from card itself, and I remember seeing some strange stats on some hardware, but I cannot remember which one it was (we were reading NULL values instead of real ones, once in a while, maybe it was a firmware issue...)