From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: Read sent/received bytes -- without opening a file in /sys or /proc Date: Thu, 17 Feb 2011 09:32:55 -0800 Message-ID: <4D5D5BC7.50802@candelatech.com> References: <4D5CFF19.6050400@googlemail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: Jan-Philip gehrcke Return-path: Received: from mail.candelatech.com ([208.74.158.172]:36364 "EHLO ns3.lanforge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751599Ab1BQRc7 (ORCPT ); Thu, 17 Feb 2011 12:32:59 -0500 In-Reply-To: <4D5CFF19.6050400@googlemail.com> Sender: netdev-owner@vger.kernel.org List-ID: On 02/17/2011 02:57 AM, Jan-Philip gehrcke wrote: > Dear list, > > I'm about to write a small C program for measurements of the bandwidth > on some network interface of my home router (uname -a: Linux > fritz.fonwlan.box 2.6.19.2 #2 Thu Nov 18 16:35:17 CET 2010 mips > GNU/Linux). I would like to accomplish very *precise* results, while > keeping the absolute measurement time low. > > In general, this problem requires the knowledge of time and byte > differences. Therefore, two time measurements and two byte counter > measurements for each, received and sent bytes, are required. Currently, > I am measuring time via > > clock_gettime(CLOCK_MONOTONIC, ...) > > and reading the byte counters by reading files in sysfs, e.g. > > /sys/class/net/${interface}/statistics/rx_bytes. > > This is very easy and works well, but reading these files four times > takes some (varying) time* on my device, which introduces an error to my > calculation. > > Hence, I am wondering, if there is a way to receive this kind of data > directly and much faster, via "kernel API". My question is related to > this unanswered one from 2005: > http://linux.derkeiler.com/Mailing-Lists/RedHat/2005-02/0557.html > > *On my device, reading such a file and interpreting the result as > integer takes 1-10 ms, measured via: > > clock_gettime(CLOCK_MONOTONIC,&t_start); > rx_bytes = read_int_from_file("/sys/class/net/wan/statistics/rx_bytes"); > clock_gettime(CLOCK_MONOTONIC,&t_end); > > read_int_from_file() basically consists of fopen(), fgets(), and sscanf(). > > > Please note that I don't have kernel/driver programming experience so far. > > Thank you for help and any suggestions! > > Jan-Philip Gehrcke The netlink API can get stats for you, but I don't know if it would be any more accurate time-wise. It's not exactly trivial to implement this API, but you can look at the 'ip' program to get an idea: git clone git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git There is also /proc/net/dev, but that may be worse than using sysfs as far as performance and time accuracy goes. Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com