From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 24F6AC433EF for ; Sun, 17 Oct 2021 11:22:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F04146124F for ; Sun, 17 Oct 2021 11:22:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245469AbhJQLZB (ORCPT ); Sun, 17 Oct 2021 07:25:01 -0400 Received: from mail-ssdrsserver2.hostinginterface.eu ([185.185.85.90]:56798 "EHLO mail-ssdrsserver2.hostinginterface.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241903AbhJQLY7 (ORCPT ); Sun, 17 Oct 2021 07:24:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=bobbriscoe.net; s=default; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=0UA4tXlXVjxMRLtbcPxYVdZJf8ukkS6nBk3kdL6DRRc=; b=Wc9uFj4XNqs4mgiOmIb51X0be0 rO/KPExfl+YUPgwLO0qo2U/KqusnXsHx0ryefmSJ6jtu8iM8h3DWd4aQd7KTXqA6urWynmwWYZLFx ZDIHPs7t0Kr7b5a4ovTBoMVWD9XajT3zJxZQOCErWh7RQcm+E1LvBDpZF22bZvcXDXOsxVlrnyDsd iuH6nqePn/Nvbg2tydACCws1YAiL7vvFrumKlt+6spiJDOU3Y+JmCRHpvvZ8YwBbD5lMkTFZExsjH +XblAuL60zxNYS2Gxn9Cpd8ZXcIqyKv5/d1Z3zInF5s+PRfvaB259LvWA0ca67KfesDbc03JI0yeV YdF6TCzw==; Received: from 67.153.238.178.in-addr.arpa ([178.238.153.67]:38292 helo=[192.168.1.11]) by ssdrsserver2.hostinginterface.eu with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94.2) (envelope-from ) id 1mc4Fc-002nau-Ce; Sun, 17 Oct 2021 12:22:48 +0100 Subject: Re: [PATCH net-next 2/2] fq_codel: implement L4S style ce_threshold_ect1 marking To: Jonathan Morton Cc: Eric Dumazet , Eric Dumazet , "David S . Miller" , Jakub Kicinski , netdev , Neal Cardwell , Ingemar Johansson S , Tom Henderson , =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= References: <20211014175918.60188-1-eric.dumazet@gmail.com> <20211014175918.60188-3-eric.dumazet@gmail.com> <87wnmf1ixc.fsf@toke.dk> <87mtnb196m.fsf@toke.dk> <308C88C6-D465-4D50-8038-416119A3535C@gmail.com> From: Bob Briscoe Message-ID: <9ad3a249-1950-c665-5996-e15352867924@bobbriscoe.net> Date: Sun, 17 Oct 2021 12:22:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <308C88C6-D465-4D50-8038-416119A3535C@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - ssdrsserver2.hostinginterface.eu X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - bobbriscoe.net X-Get-Message-Sender-Via: ssdrsserver2.hostinginterface.eu: authenticated_id: in@bobbriscoe.net X-Authenticated-Sender: ssdrsserver2.hostinginterface.eu: in@bobbriscoe.net X-Source: X-Source-Args: X-Source-Dir: Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 16/10/2021 08:39, Jonathan Morton wrote: >> On 15 Oct, 2021, at 2:24 am, Toke Høiland-Jørgensen wrote: >> >>>>> Add TCA_FQ_CODEL_CE_THRESHOLD_ECT1 boolean option to select Low Latency, >>>>> Low Loss, Scalable Throughput (L4S) style marking, along with ce_threshold. >>>>> >>>>> If enabled, only packets with ECT(1) can be transformed to CE >>>>> if their sojourn time is above the ce_threshold. >>>>> >>>>> Note that this new option does not change rules for codel law. >>>>> In particular, if TCA_FQ_CODEL_ECN is left enabled (this is >>>>> the default when fq_codel qdisc is created), ECT(0) packets can >>>>> still get CE if codel law (as governed by limit/target) decides so. >>>> The ability to have certain packets receive a shallow marking threshold >>>> and others regular ECN semantics is no doubt useful. However, given that >>>> it is by no means certain how the L4S experiment will pan out (and I for >>>> one remain sceptical that the real-world benefits will turn out to match >>>> the tech demos), I think it's premature to bake the ECT(1) semantics >>>> into UAPI. >>> Chicken and egg problem. >>> We had fq_codel in linux kernel years before RFC after all :) >> Sure, but fq_codel is a self-contained algorithm, it doesn't add new >> meanings to bits of the IP header... :) > I'll be blunter: > > In its original (and currently stable) form, fq_codel is RFC-compliant. It conforms, in particular, to RFC-3168 (ECN). There's a relatively low threshold for adding RFC-compliant network algorithms to Linux, and it is certainly not required to have a published RFC specifically describing each qdisc's operating principles before it can be upstreamed. It just so happens that fq_codel (and some other notable algorithms such as CUBIC) proved sufficiently useful in practice to warrant post-hoc documentation in RFC form. > > However, this patch adds an option which, when enabled, makes fq_codel *non-compliant* with RFC-3168, specifically the requirement to treat ECT(0) and ECT(1) identically, unless conforming to another published RFC which permits different behaviour. > > There is a path via RFC-8311 to experiment with alternative ECN semantics in this way, but the way ECT(1) is used by L4S is specifically mentioned as requiring a published RFC for public deployments. The L4S Internet Drafts have *just failed* an IETF WGLC, which means they are *not* advancing to publication as RFCs in their current form. [BB] Clarification of IETF process: A first Working Group Last Call (WGLC) is nearly always the beginning of the end of the IETF's RFC publication process. Usually the majority of detailed comments arrive during a WGLC. Then the draft has to be fixed, and then it goes either directly through to the next stage (in this case, an IETF-wide last call), or to another WGLC. > The primary reason for this failure is L4S' fundamental incompatibility with existing Internet traffic, despite its stated goal of general Internet deployment. [BB] s/The primary reason /JM's primary objection / There is no ranking of the reasons for more work being needed.  The WG had already developed a way to mitigate this objection. Otherwise, a WGLC would not have been started in the first place. Further work on this issue is now more likely to be wordsmithing. I hope this level of brevity was useful for netdev. See tsvwg@ietf.org for details. Bob > It is my considered opinion, indeed, that moving *away* from ECT(1) as the L4S identifier is the best option for improving that compatibility. > > I believe there is a much higher threshold required for adding such things to publicly maintained versions of Linux (as opposed to privately maintained experimental versions). > > - Jonathan Morton -- ________________________________________________________________ Bob Briscoe http://bobbriscoe.net/