From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ip-64-139-1-69.sjc.megapath.net (ip-64-139-1-69.sjc.megapath.net [64.139.1.69]) by huchra.bufferbloat.net (Postfix) with ESMTP id 1886821F151 for ; Sun, 1 Dec 2013 21:45:26 -0800 (PST) Received: from shuksan (localhost [127.0.0.1]) by ip-64-139-1-69.sjc.megapath.net (Postfix) with ESMTP id 523C0406060; Sun, 1 Dec 2013 21:45:26 -0800 (PST) X-Mailer: exmh version 2.7.2 01/07/2005 with nmh-1.3 To: bloat-devel@lists.bufferbloat.net From: Hal Murray Subject: Re: One-way delay measurement for netperf-wrapper Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Sun, 01 Dec 2013 21:45:26 -0800 Message-Id: <20131202054526.523C0406060@ip-64-139-1-69.sjc.megapath.net> X-BeenThere: bloat-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: "Developers working on AQM, device drivers, and networking stacks" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 02 Dec 2013 05:45:27 -0000 toke@toke.dk said: > - Is clock drift something to worry about over the timescales of these > tests? It depends. :) How long are you running the tests? How accurate do you expect the timings to be? ntpd assumes the network delays are symmetric. It's easy to break that assumption by sending a lot of traffic in one direction. ntpd tries to avoid that problem. It remembers the last 8 packets to a server and uses the one with the shortest round trip time. If you run tests for long enough you will overflow that buffer. The time scale is somewhere between minutes and hours. -- These are my opinions. I hate spam.