From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756090AbZEEFFB (ORCPT ); Tue, 5 May 2009 01:05:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751561AbZEEFEs (ORCPT ); Tue, 5 May 2009 01:04:48 -0400 Received: from 1wt.eu ([62.212.114.60]:4269 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751515AbZEEFEr (ORCPT ); Tue, 5 May 2009 01:04:47 -0400 Date: Tue, 5 May 2009 07:04:37 +0200 From: Willy Tarreau To: Matthias Saou Cc: Eric Dumazet , linux-kernel@vger.kernel.org, Linux Netdev List Subject: Re: Wrong network usage reported by /proc Message-ID: <20090505050435.GK570@1wt.eu> References: <20090504171408.3e13822c@python3.es.egwn.lan> <49FF2BB2.4030700@cosmosbay.com> <20090504211151.74622f29@python3.es.egwn.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20090504211151.74622f29@python3.es.egwn.lan> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 04, 2009 at 09:11:51PM +0200, Matthias Saou wrote: > Eric Dumazet wrote : > > > Matthias Saou a écrit : > > > Hi, > > > > > > I'm posting here as a last resort. I've got lots of heavily used RHEL5 > > > 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. > > > > > > For some details and a test script which compares values from /proc > > > with values from tcpdump : > > > https://bugzilla.redhat.com/show_bug.cgi?id=489541 > > > > > > The values collected using tcpdump always seem realistic and match the > > > values seen on the remote network equipments. So my obvious conclusion > > > (but possibly wrong given my limited knowledge) is that something is > > > wrong in the kernel, since it's the one exposing the /proc interface. > > > > > > 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. The > > > simple python script available here allows to see it quite easily : > > > https://www.redhat.com/archives/rhelv5-list/2009-February/msg00166.html > > > > > > * 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 > > > > > > 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. > > > > > > Matthias > > > > > > > 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...) > > My workstation has a Broadcom BCM5752 (tg3 module). The servers which > are most affected have Intel 82571EB (e1000e). But the issue is that > with /proc, the values are a lot _higher_ than with tcpdump, and the > tcpdump values seem to be the correct ones. the e1000 chip reports stats every 2 seconds. So you have to collect stats every 2 seconds otherwise you get "camel-looking" stats. Willy