From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-x232.google.com (mail-lj1-x232.google.com [IPv6:2a00:1450:4864:20::232]) (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 B4BA83B29D for ; Thu, 7 May 2020 04:09:22 -0400 (EDT) Received: by mail-lj1-x232.google.com with SMTP id u15so5312769ljd.3 for ; Thu, 07 May 2020 01:09:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=1kdPeUtzZ979qjAq3Ise81WDksHwKCRt1onTuTHjX4c=; b=HZW2A20h9ttr0lN3ZO6T7RG9fm/YeXAfQ2/+SQ77k6te7OTed1WnXC7K3n6R7K+EMT lmC/K+FIdkwVulOxjrbjPa98L74RC8jyjdRGdDSkcy7oAEF+WR1ar5X2Dsena1BsI6de tVE3ABBFInR/IguM1SxeNMj2pBEnbIFBJD5lLoJ/FQTKNDs4qmj6iIBiGEH+D1O1mfD0 dKnnLoF8Nv0CIlVryi81/lhbIfsVJCtuqoAp+3zCcRtGDirAYYo89Aijf04+ecKJeF6H WzpwrTQ9jAJhcpTuadBGT9JEgz32as3q6NvI+TYy6IGRBXQVmwJU4zU5CulZbzNlhLLz uGGg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=1kdPeUtzZ979qjAq3Ise81WDksHwKCRt1onTuTHjX4c=; b=lP022i3i6Jl4132LQOiZdi2jKoA9k+Y4NJBoPLQarnoj9kXLGLdrazKDVKFtdSp2K9 a+GS51VIEqtiPNGfKagEIbmXi6Vuo1FRQ8CAK7uIb+2RBTfTHgWAVqv8wvgQLPSKMl8h T4IRfKKnAL7V/PKbxth6LOaZd3wdOOGi+5ZbqcIlaCAB+8uxdNl8ajERaFtSGFtPZvh2 Wm2d6JMl8OApLZgZSycXK7CFtQidqM3AZZh9fX/GiUfLz+CXU1U/NwpY/GGXKCN8xmZK kHREwDZB/RRWn5x45cLg0HIj2FsFRWYXsz519yYMzbGHBI12kxA0zJ7FlX3ykuGQ6hFX bLQw== X-Gm-Message-State: AGi0PuZgPdimZd7eKUpwJHa0ha3SgG15381ha3VFk4vyB+6dBv2ZPXT8 1A5iMUbVCXeOCUsj11lNEzUp1nau X-Google-Smtp-Source: APiQypJ206NnFDKlzUMUWCm303b7kToajoqhFllvuLzhcsNCpwlWvs/wlHmn2IabOpWbXqX0eQW2ng== X-Received: by 2002:a2e:96c2:: with SMTP id d2mr7826045ljj.214.1588838961587; Thu, 07 May 2020 01:09:21 -0700 (PDT) Received: from jonathartonsmbp.lan (83-245-235-192-nat-p.elisa-mobile.fi. [83.245.235.192]) by smtp.gmail.com with ESMTPSA id g22sm2800022ljl.17.2020.05.07.01.09.20 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 07 May 2020 01:09:21 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) From: Jonathan Morton In-Reply-To: Date: Thu, 7 May 2020 11:09:19 +0300 Cc: Cake List Content-Transfer-Encoding: quoted-printable Message-Id: References: To: Kevin Darbyshire-Bryant X-Mailer: Apple Mail (2.3445.9.1) Subject: Re: [Cake] Latency target curiosity 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: Thu, 07 May 2020 08:09:23 -0000 > On 7 May, 2020, at 10:58 am, Kevin Darbyshire-Bryant = wrote: >=20 > A curiosity has arisen: I use diffserv4 mode on a 20Mbit egress link. = Bulk tin has =E2=80=98capacity=E2=80=99 threshold of 1.2Mbit and = because it=E2=80=99s a slow =E2=80=99tin', the default target & interval = values get overridden to 14.6ms and 109.6ms respectively. The 3 other = tins are 5ms & 100ms defaults. >=20 > I have a backup job that bulk uploads 5 simultaneous flows to = Onedrive. The sparse_delay, average_delay & peak_delay figures settle = on 32, 38 & 43 ms respectively with around 9 drops per second on that = tin. >=20 > I=E2=80=99m curious as to why the reported delays are over double the = target latency? It's likely that there's a minimum cwnd in your sender's TCP stack, = which may be as large as 4 segments. In Linux it is 2 segments. No = matter how much congestion signalling is asserted, the volume of data in = flight (including retransmissions of dropped packets) will always = correspond to at least that minimum per flow. If the path is short, = most of that volume will exists in queues instead of on the wire. Fortunately, backups are unlikely to suffer from a small amount of extra = latency, and Cake will isolate their influence from other flows that may = be more sensitive. - Jonathan Morton