From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-x22b.google.com (mail-lf0-x22b.google.com [IPv6:2a00:1450:4010:c07::22b]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 820CB3B2BC; Sat, 4 Jun 2016 09:55:55 -0400 (EDT) Received: by mail-lf0-x22b.google.com with SMTP id b73so70204415lfb.3; Sat, 04 Jun 2016 06:55:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=Pyl2AS9x/DaA0NT92vmMwgqxjnw29PSj+us1S8du0EU=; b=zn7Ong4hTcdae8i3gZCo/liFMye3/Em+kqQjqiIRlkyx+Pwg7H4rx8m+g+f7U9KTnK dS8v/dK1l/vOmF40OOug4wTy/qRg/LDsOj1g0YFZGtSffDTf1MNSHoRzD4vZ9fcFCmZC tCRRFf+MRsfAzh9SYD/XmnwitOtgUnJTiNGAygnPHn8q5vVfVFTx3rPcxfj/fCn+T+zg +W+duyUV7KMpuqdqTKdv2MsyU59/ecH27vDdAYqMpgDHLVLWklopeZXP3q0m5SsMfq8P xGDUFaFXXciJtUxZXCu6ytKJ6M81PmcjuTmFlL5WYJ47kVghhxQNHWPC7iep5iu/9ooS ZdHQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=Pyl2AS9x/DaA0NT92vmMwgqxjnw29PSj+us1S8du0EU=; b=C04g4UPGVWB2EFNfB/NqYxXaIZRW+RfOVHnnW994IvRuT9YK0A8pK2I4Ct5t5xx5ZC IO5h1CU3GXCnrs7bECx4EY4h658Z9oz7ibkmm46+iSmOLD5sqUy+2ctKXRMEfYyMKlPJ Yr79CHuGes24Eo7WfOVOb7ilreMtKFsSiCGWq+bTwGXSb+stOO+tgSmPmB0z1WQdL1tP E/IcXrb/5ktnc2bMZ3SapSqWKr5ATk/CPZ7KxQp1M/IyUw4wD69niliaMEPCZrxzPtOq y+xM5boEhQ4TWZ5hQFkTrcwbWA+IBecjXv515TqiWXFe+5MDAcvVb1K4yK/CRGOvSUO6 A6PQ== X-Gm-Message-State: ALyK8tJsQ87Nq14eA1G/Ctf1IRWSHownbKUw8ZiMujKYXvsXAC2t9EPcsRnMo2/mjkymhg== X-Received: by 10.25.146.66 with SMTP id u63mr1962545lfd.42.1465048553974; Sat, 04 Jun 2016 06:55:53 -0700 (PDT) Received: from bass.home.chromatix.fi (37-33-56-85.bb.dnainternet.fi. [37.33.56.85]) by smtp.gmail.com with ESMTPSA id re2sm949923lbb.22.2016.06.04.06.55.52 (version=TLSv1/SSLv3 cipher=OTHER); Sat, 04 Jun 2016 06:55:53 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) From: Jonathan Morton In-Reply-To: Date: Sat, 4 Jun 2016 16:55:50 +0300 Cc: Noah Causin , cake@lists.bufferbloat.net, "codel@lists.bufferbloat.net" Content-Transfer-Encoding: quoted-printable Message-Id: <01BEA343-7C07-46FA-8DC4-07BF26309FC8@gmail.com> References: <22371476-B45C-4E81-93C0-D39A67639EA0@gmx.de> <857AEE56-E7DB-4981-B32E-82473F877139@gmail.com> <8AB0D25D-C1CA-45F1-889E-2F73CF8C44F7@gmail.com> <323AFC22-A092-4F59-8197-AF21EF73FD58@gmail.com> <274D3A0FA900FD47AA6B56991AAA32FDC5529FC8@wtl-exchp-1.sandvine.com> <574478B4.7080103@taht.net> <39F38477-A877-4C1B-9B7F-BB3358425F17@gmail.com> <0eb223f9-2873-7f53-c2ce-c6867ddec17c@gmail.com> <48A25043-19E2-4BB7-B634-A4003F7BE6F8@gmail.com> To: Andrew McGregor X-Mailer: Apple Mail (2.3124) Subject: Re: [Cake] [Codel] Proposing COBALT X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 04 Jun 2016 13:55:55 -0000 > On 4 Jun, 2016, at 04:01, Andrew McGregor = wrote: >=20 > ...servers with ECN response turned off even though they negotiate = ECN. It appears that I=E2=80=99m looking at precisely that scenario. A random selection of connections from a packet dump show very high = marking rates, which are apparently acknowledged using CWR, but a = subsequent dropped packet (probably due to queue overflow) takes many = seconds to be retransmitted (I=E2=80=99m using a rather high memory = limit for observation purposes). Overall the TCP behaviour is approximately normal for NewReno on a dumb = FIFO, and the ECN signalling is completely ignored. This doesn=E2=80=99t = rule out the possibility that it=E2=80=99s a different Reno relative, = such as Westwood+ or Compound. There=E2=80=99s often more than one CWR per RTT. This isn=E2=80=99t a = consistent characteristic; some connections have normal-looking CWRs = while others issue them every three packets, as if they=E2=80=99re = fishing for =E2=80=9Cmore accurate=E2=80=9D ECN feedback. It might vary = by host; I didn=E2=80=99t keep track of that. But this can=E2=80=99t be = DCTCP; even that should back off in the face of a 100% marking rate, = which is often achieved at my low bandwidth and with very persistent = queues. Other servers respond normally to ECN signals, ruling out interference = by my ISP. It=E2=80=99s possible the ECE flag is wiped and the CWRs are = faked, but there=E2=80=99s no legitimate reason to do that. The CWRs = ultimately make no difference, since at 100% CE marks, every ack has ECE = set anyway. Turning off ECN negotiation at the client results in a much better = managed queue with similar throughput. It=E2=80=99s not immediately = obvious whether that=E2=80=99s due to a functioning congestion response = or simply the AQM clearing out the queue the hard way. It=E2=80=99ll be = interesting to see what effect COBALT has here, when I get it to = actually work. As for who these servers are: Valve Software=E2=80=99s Steam platform. = I did say they were large and popular. - Jonathan Morton