From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from masada.superduper.net (unknown [IPv6:2001:ba8:1f1:f263::2]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id D7F3D21F118 for ; Wed, 27 Mar 2013 16:34:09 -0700 (PDT) Received: from snappy-wlan.parc.xerox.com ([13.1.108.21]) by masada.superduper.net with esmtpsa (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.72) (envelope-from ) id 1UKzr4-00050g-9W for codel@lists.bufferbloat.net; Wed, 27 Mar 2013 23:34:06 +0000 Message-ID: <515381EB.8030709@superduper.net> Date: Wed, 27 Mar 2013 16:34:03 -0700 From: Simon Barber User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130308 Thunderbird/17.0.4 MIME-Version: 1.0 To: codel@lists.bufferbloat.net Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -2.9 (--) Subject: [Codel] sawtooth X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Mar 2013 23:34:10 -0000 I've been thinking about codel's behaviour with a single TCP stream. TCP in steady state exhibits a sawtooth cwin behaviour. cwind rises by 1 each RTT until the queue drops a packet, then cwind halves, and repeat. With codel the earliest a packet will be dropped is 100ms after the queue size grows to the point the sojourn is 5ms. At this point the cwin is halved. For small RTTs or with multiple flows this may ensure good utilisation, but for large RTTs and a single flow surely dropping this early could result in starvation? Simon