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 X-Spam-Level: X-Spam-Status: No, score=-14.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 86811C43331 for ; Tue, 24 Mar 2020 17:05:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 540B72076F for ; Tue, 24 Mar 2020 17:05:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="IntQvyZT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727366AbgCXRFz (ORCPT ); Tue, 24 Mar 2020 13:05:55 -0400 Received: from mail-vs1-f65.google.com ([209.85.217.65]:34302 "EHLO mail-vs1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726962AbgCXRFz (ORCPT ); Tue, 24 Mar 2020 13:05:55 -0400 Received: by mail-vs1-f65.google.com with SMTP id b5so1194726vsb.1 for ; Tue, 24 Mar 2020 10:05:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=++YignfeluUqAX6pApRaB75AO87QYP7h18KmSFM05EQ=; b=IntQvyZT/D4wnOdtnjvZ9EDnZREA1vm6rsI9c4pZj6e+ZQZIfeVS+wOlrlLJMI96WI 1nckS4q1/xfOMNDp3N/jDXdksrEUbU1AFn7564IbV5EgrJABxcSm8/770t2mt83RTj7e wOFDI77AH0urGLOusd2YhPhyMwJ69WSIdOPl0bvjHYlyCBTSdD8UY/j3h1TKQqwkSfhN fkBCq0HqBCxcN4Kpy8fDm0CbrP3KkmgzxnMhJebEP7ejH6198e4OmqKRxpilluiUCgAE KH+6I0Rf9BfCk8COmVsW2xXZPw8ddDRjPIH6VaXZjRb9GPKF5cV2AYhqlcAaDoj/DmnU WxNA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=++YignfeluUqAX6pApRaB75AO87QYP7h18KmSFM05EQ=; b=bRmisbFZy2RRwRSWPkIctpuqw+DL665QomtMrg972/V9qeB4rEfqyjwgD2lciJ4bsQ F24YdhuEjW71tton97kXKddQTRH4WjQitVaakyGEZhkwxFFtADi4MqIf/iL5H4zfv+oN 9cK9h8JJKjR6lIuGyfJHXPQaFhxEjSUbjqKnWIne3u+dogvbl+i5dyUzYlLmedsrmcK9 FvPngzuBao2GqNaSfgK8Y0J3HQt6TM0yPvutowx+ho4RD/eEZ0iNG3rfXg4rZn+Ysy/H EHnFoYTTX53cDIVCxJkHl6AZ9dQeZmiS3tROB8yLsHJ//zc20XVqaDRwUlkElBhdH0Wh w+6A== X-Gm-Message-State: ANhLgQ0MHPwf8W9iGBW1ggGGvmLun7cgiXGiJ2XKRmKTK9d3O7Bt8zZc XTHo4ss8AHKHMM6W8rlgHK3ERcTRNz/07wXEhUWOxQ== X-Google-Smtp-Source: ADFU+vtogMt3VOC8v44d05QIPL2BfL2sDBZT5HXowVsKyIdVvGdfGeFVKo0KEFQdnROXY/uE6ryM5bjqink90i8WV8k= X-Received: by 2002:a67:70c2:: with SMTP id l185mr18912552vsc.123.1585069552882; Tue, 24 Mar 2020 10:05:52 -0700 (PDT) MIME-Version: 1.0 References: <1584524612-24470-1-git-send-email-ilpo.jarvinen@helsinki.fi> <1584524612-24470-29-git-send-email-ilpo.jarvinen@helsinki.fi> In-Reply-To: From: Yuchung Cheng Date: Tue, 24 Mar 2020 10:05:16 -0700 Message-ID: Subject: Re: [RFC PATCH 28/28] tcp: AccECN sysctl documentation To: =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= Cc: Dave Taht , Linux Kernel Network Developers , Neal Cardwell , Eric Dumazet , Olivier Tilmans Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Mar 24, 2020 at 5:50 AM Ilpo J=C3=A4rvinen wrote: > > On Mon, 23 Mar 2020, Yuchung Cheng wrote: > > > On Mon, Mar 23, 2020 at 6:34 AM Ilpo J=C3=A4rvinen > > wrote: > > > > > > On Fri, 20 Mar 2020, Yuchung Cheng wrote: > > > > > > > On Fri, Mar 20, 2020 at 3:40 PM Ilpo J=C3=A4rvinen > > > > wrote: > > > > > > > > > > On Thu, 19 Mar 2020, Dave Taht wrote: > > > > > > > > > > > On Wed, Mar 18, 2020 at 2:44 AM Ilpo J=C3=A4rvinen wrote: > > > > > > > > > > > > > > From: Ilpo J=C3=A4rvinen > > > > > > > > > > > > > > Signed-off-by: Ilpo J=C3=A4rvinen > > > > > > > --- > > > > > > > Documentation/networking/ip-sysctl.txt | 12 +++++++++--- > > > > > > > 1 file changed, 9 insertions(+), 3 deletions(-) > > > > > > > > > > > > > > diff --git a/Documentation/networking/ip-sysctl.txt b/Documen= tation/networking/ip-sysctl.txt > > > > > > > index 5f53faff4e25..ecca6e1d6bea 100644 > > > > > > > --- a/Documentation/networking/ip-sysctl.txt > > > > > > > +++ b/Documentation/networking/ip-sysctl.txt > > > > > > > @@ -301,15 +301,21 @@ tcp_ecn - INTEGER > > > > > > > 0 Disable ECN. Neither initiate nor accept E= CN. > > > > > > > 1 Enable ECN when requested by incoming conne= ctions and > > > > > > > also request ECN on outgoing connection att= empts. > > > > > > > - 2 Enable ECN when requested by incoming conne= ctions > > > > > > > + 2 Enable ECN or AccECN when requested by inco= ming connections > > > > > > > but do not request ECN on outgoing connecti= ons. > > > > > > > > > > > > Changing existing user-behavior for this default seems to be ov= erly > > > > > > optimistic. Useful for testing, but... > > > > > > > > > > I disagree. > > > > > > > > > > The kernel default on ECN is/has been "do nothing" like forever. = Yet, > > > > > passively allowing ECN on servers is a low risk operation because= nothing > > > > > will change before client actively asks for it. However, it was o= bvious > > > > > that the servers didn't do that. The servers could have set tcp_e= cn to 1 > > > > > (before 2 was there) which is low risk for _servers_ (unlike for = clients) > > > > > but only very very few did. I don't believe servers would now > > > > > intentionally pick 2 when they clearly didn't pick 1 earlier eith= er. > > > > > > > > > > Adding 2 is/was an attempt to side-step the need for both ends to= make > > > > > conscious decision by setting the sysctl (which servers didn't wa= nt to > > > > > do). That is, 2 gives decision on what to do into the hands of th= e client > > > > > side which was the true intent of 2 (in case you don't know, I ma= de that > > > > > change). > > > > What can a server configure to process only RFC3168 ECN if it prefe= rs to? > > > > > > That's why I suggested the flag-based approach? > > > > That's assuming an admin that has control of sysctls can also change > > individual applications (easily). In reality it often is not the case. > > The default sysctl choices in this patch seem risky to me. > > > > > > > If "full control" is the way to go, I think it should be made usi= ng flags > > > > > instead, along these lines: > > > > > > > > > > 1: Enable RFC 3168 ECN in+out > > > > > 2: Enable RFC 3168 ECN in (default on) > > > > > 4: Enable Accurate ECN in (default on) > > > > > 8: Enable Accurate ECN in+out > > > > > > > > > > Note that I intentionally reversed the in and in/out order for 4&= 8 > > > > > (something that couldn't be done with 1&2 to preserve meaning of = 1). > > > > > > It should address any except "out" but no "in" (the meaning of 1 cann= ot > > > be changed I think). But out w/o in doesn't sound very useful. > > So you mean you'd want to have control that is finer-grained than what th= e > sysctls offer? I recommend having separate sysctl values for AccECN so that servers configured to use existing values do not behave differently (on ECN) after kernel upgrade, similar to what Dave Taht suggested. > > > -- > i.