From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-x22f.google.com (mail-qg0-x22f.google.com [IPv6:2607:f8b0:400d:c04::22f]) (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 367033B25D; Sun, 1 May 2016 14:46:28 -0400 (EDT) Received: by mail-qg0-x22f.google.com with SMTP id f92so61732929qgf.0; Sun, 01 May 2016 11:46:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=message-id:subject:from:to:cc:date:in-reply-to:references :mime-version:content-transfer-encoding; bh=1ZMo0XV/2hAhWGNWX/d8Gfhl+62mHPcjBoRAoCjeUkg=; b=VUzlPIrq/8svelfiz1wa7FcLEzZR082A0IimNGmED80OZf8ZCZKarlVzxmvaj/JbAX jm3yeId5NCVv5aFVBhklvcH1d4ogaeF09WoE7yUMEUwU8srz9fJXWW+0GYiCAlWYE7/A A4lIeke1REP1WGTOiZ8iJA6mSC17xh/h/80rsuiBBCc5yBsV7MsPFsIQM+BMlPqTMoaY IvgPy/aYHv5keYe7Tui/7Sf5f2VISaRuM4YzWb17PEy/n/7/DeXYaQezerlXq5RRWxdf ijroNWMG+feMWSTmLPqizSs0gN8uedoEptAL32FTaquNJ5dTD1j90WdAqiYr42g5jEWf /dDw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:message-id:subject:from:to:cc:date:in-reply-to :references:mime-version:content-transfer-encoding; bh=1ZMo0XV/2hAhWGNWX/d8Gfhl+62mHPcjBoRAoCjeUkg=; b=klYutz0S/btbJy4ykxdPOH/8L+8LEKPslA/30YGS5G/4M3HFggjebnMFmULzZr2wsR 7p9ZE4gxR4lbJ6+M7Y2/aOlUlGupfQ+l8lhQWXNc05cN+5RNjNbXgK4REqFoRjzx1mAt E0wrBdxUfZz5oVURNj5dTwj65fPxRj8jKA0I5wNijU7z0utUdST4VL9sKwsNZ4JT7Fb4 5pEWWRszAbRvmfL+bKWMTGAtjalOj66eoDtSXm++Q4UDZRGvJwU0xgi/3tD7DacDN7XO h90Pj00hydTrHOjql/PuosSn8diHzTSuvI2ZWw2tHnhH5dqzkF+gmj1AmtkrRLvobglC I30w== X-Gm-Message-State: AOPr4FVInOAgi40RfFzGwkmVob8SNKHwIlxQ3o+CuxgjjheMjKgYGgoHOYhQ2NHL9KCpWA== X-Received: by 10.140.145.82 with SMTP id 79mr29932718qhr.95.1462128387862; Sun, 01 May 2016 11:46:27 -0700 (PDT) Received: from [100.96.106.16] ([100.96.106.16]) by smtp.googlemail.com with ESMTPSA id a207sm7957435qkb.28.2016.05.01.11.46.26 (version=TLSv1/SSLv3 cipher=OTHER); Sun, 01 May 2016 11:46:27 -0700 (PDT) Message-ID: <1462128385.5535.200.camel@edumazet-glaptop3.roam.corp.google.com> From: Eric Dumazet To: Jonathan Morton Cc: Dave Taht , make-wifi-fast@lists.bufferbloat.net, "codel@lists.bufferbloat.net" , ath10k Date: Sun, 01 May 2016 11:46:25 -0700 In-Reply-To: <865DA393-262D-40B6-A9D3-1B978CD5F6C6@gmail.com> References: <1462125592.5535.194.camel@edumazet-glaptop3.roam.corp.google.com> <865DA393-262D-40B6-A9D3-1B978CD5F6C6@gmail.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-Mailman-Approved-At: Mon, 02 May 2016 15:49:25 -0400 Subject: Re: [Make-wifi-fast] [Codel] fq_codel_drop vs a udp flood X-BeenThere: make-wifi-fast@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 01 May 2016 18:46:28 -0000 On Sun, 2016-05-01 at 21:20 +0300, Jonathan Morton wrote: > > On 1 May, 2016, at 20:59, Eric Dumazet wrote: > > > > fq_codel_drop() could drop _all_ packets of the fat flow, instead of a > > single one. > > Unfortunately, that could have bad consequences if the “fat flow” > happens to be a TCP in slow-start on a long-RTT path. Such a flow is > responsive, but on an order-magnitude longer timescale than may have > been configured as optimum. Are you trying to reinvent Hystart ? ;) > > The real problem is that fq_codel_drop() performs the same (excessive) > amount of work to cope with a single unresponsive flow as it would for > a true DDoS. Optimising the search function is sufficient. Optimizing the search function is not possible, unless you slow down the fast path. This was my design choice. Just drop half backlog packets instead of 1, (maybe add a cap of 64 packets to avoid too big burts of kfree_skb() which might add cpu spikes) and problem is gone. TCP in slow start wont be hurt at all. A fat TCP flow is still fat. Only bad CC could possibly be hurt.