From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-x22c.google.com (mail-lf0-x22c.google.com [IPv6:2a00:1450:4010:c07::22c]) (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 0D7FA3BA8E for ; Wed, 25 Apr 2018 12:52:07 -0400 (EDT) Received: by mail-lf0-x22c.google.com with SMTP id d20-v6so26478458lfe.3 for ; Wed, 25 Apr 2018 09:52:07 -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=pMuVUlefl+6ojsDUvAUwo8VE6lURnGsST3tirF3NCDY=; b=sL5loqa4nAlpXa9jk7Qn6zG9NWuEr4qA+0OfWVdGZxmsnA9kWiT03lydcOMZbUXn2c Tj53Puy43tcxcnzqs55Du+H/5Iun5sih3xyffagErAZCmOE51U+zf7gMggG/la8uDjFr wA7t0mhI0HCeX4/odppt9ppOl2f+R2M58G6piH2YlJrYRox9UJHekJ5zw3hh+qCh8Jq5 aFLNjHU++CZsgBdl4VqeCMuFeJr8KjAUDDijbeKUw2qMRaBhmu/j02oMU8hl7elxL2yM boyA1mUjU69PbL5HFqtCGIXvtcclZo7qk0zN8k7pGhvDOMlxSmSv+Icz04TpyTwhAwZ3 0GOA== 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=pMuVUlefl+6ojsDUvAUwo8VE6lURnGsST3tirF3NCDY=; b=sG8GqmyMXXeYyFvZ9bWCriuZABzWcpRXFEG+046qyBqrf/TWr6SpHUsqxVshhoaRN7 0BH12642QkGUAwB2fjbaOfyVsdgulEc4is5SfZFsVcKfuTnbE91Elt9EnQuJ6higyhTp Rhlcp36Voe18/W9S//I9+Ti8c2JOTweNLfEL0XYH2V7y9xKvBR9VJddlkpu2yHsSJwpR VEL/FIoX1Og5F9fgNde32wj2rtMWWFCrx9Ty3GbNm2a99yG4LAlLyWAS3g/YpAzZf+yb TREzYj4u3dsQVTXSYU6tF0Amrr3vuyShhElsMp7Nu7OYBrKltXcmNCX7CXjdTH08rRhQ 3d/w== X-Gm-Message-State: ALQs6tA3JrynXACt/vlZ2jUvmpQqsNJSxhzih5GJLx9XKfKnJTHO5Rgd IehX8LIFEDKybOhp5d34HXU= X-Google-Smtp-Source: AB8JxZoWq8BWgnL9xtZOVlh8qv9U3Dfqs3uwAfC61Y7TBJSS5NMxWIlJiaiqGn40iWS6g+u5ILm88Q== X-Received: by 2002:a19:b217:: with SMTP id b23-v6mr2065886lff.51.1524675126880; Wed, 25 Apr 2018 09:52:06 -0700 (PDT) Received: from [192.168.239.216] (83-245-234-255-nat-p.elisa-mobile.fi. [83.245.234.255]) by smtp.gmail.com with ESMTPSA id g25sm3336915ljf.63.2018.04.25.09.52.05 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 25 Apr 2018 09:52:06 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 11.3 \(3445.6.18\)) From: Jonathan Morton In-Reply-To: <8bae2ee1-efcc-1571-2a30-5b7779de2c88@gmail.com> Date: Wed, 25 Apr 2018 19:52:03 +0300 Cc: =?utf-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= , netdev@vger.kernel.org, cake@lists.bufferbloat.net Content-Transfer-Encoding: quoted-printable Message-Id: References: <20180425134249.21300-1-toke@toke.dk> <878t9b5n0q.fsf@toke.dk> <6bc11ded-028f-6c8f-964e-a569b4e10813@gmail.com> <8736zj6zj2.fsf@toke.dk> <8bae2ee1-efcc-1571-2a30-5b7779de2c88@gmail.com> To: Eric Dumazet X-Mailer: Apple Mail (2.3445.6.18) Subject: Re: [Cake] [PATCH net-next v3] Add Common Applications Kept Enhanced (cake) qdisc 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: Wed, 25 Apr 2018 16:52:08 -0000 > We can see here the high cost of forcing software GSO :/ >=20 > Really, this should be done only : > 1) If requested by the admin ( tc .... gso ....) >=20 > 2) If packet size is above a threshold. > The threshold could be set by the admin, and/or based on a fraction = of the bandwidth parameter. >=20 > I totally understand why you prefer to segment yourself for < 100 Mbit = links. >=20 > But this makes no sense on 10Gbit+ It is absolutely necessary, so far as I can see, to segment GSO = superpackets when overhead compensation is selected - as it very often = should be, even on pure Ethernet links. Without that, the calculation = of link occupancy time will be wrong. (The actual transmission time of = an Ethernet frame is rather more than just 14 bytes longer than the = underlying IP packet.) Another reason to apply GSO segmentation is to achieve maximal = smoothness of flow isolation. This should still be achievable within = some tolerance at high link rates, but calculating this tolerance is = complicated by the triple-isolate algorithm. If there's a way to obtain the individual packet sizes without incurring = the full segmentation overhead, it may be worth considering (at high = link rates only). I would want to leave it on by default, because some = of Cake's demonstrably superior latency performance depends on seeing = the real packets, not the aggregates, and the overhead only becomes = significant above 100Mbps on weak MIPS CPUs and 1Gbps on vaguely modern = x86 stuff. - Jonathan Morton