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=-5.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 CB5C0C0650F for ; Thu, 8 Aug 2019 06:12:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9C7952186A for ; Thu, 8 Aug 2019 06:12:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="H3CQAuen" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731031AbfHHGMs (ORCPT ); Thu, 8 Aug 2019 02:12:48 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:46206 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730694AbfHHGMs (ORCPT ); Thu, 8 Aug 2019 02:12:48 -0400 Received: by mail-wr1-f67.google.com with SMTP id z1so93648350wru.13 for ; Wed, 07 Aug 2019 23:12:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=U0s/TE2KV6UWHDtgqwRw1jB8OvUt1IQe30q53AHk1hk=; b=H3CQAuen1EN6ba8KcVUfBquRIXKgMyFmmG0Oe5AklCEic1U0eG2IYi1ZcprGtsDQtq F+EvOHn+chHntsC+hMgberUR8vB3J4C70a7JF6//uj0erRQreyGPPADQXI8NG8mehwY9 vPB0SjugZyUOsE8IaWFoC8sUmKTYhHpZbygOHihRGalsTM3M1mkCFCgbFaPYc8vweO2v B55ygvboV1r2AReCiszkvZewhQ7noQtzzhogWtATaQkVlrBggDiNvw3zMkvHp9G3gEa/ R/YmDxDWTRkZrkkRD1OCbt17sa3lmzexV1ammBJHm6uZSaPdw743617t3TE34pQbGV5O wt1A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=U0s/TE2KV6UWHDtgqwRw1jB8OvUt1IQe30q53AHk1hk=; b=XeoYCpzQanu9QkGpLHWsTjnXA6Ez7rPl5as8Rt+r/rLDmT8CtgFVK8u4p2mg4NN5QM fZO6GKB8WA3m6boeh2VtQ0qY6eF6Hl4I8mUGOrvlFZ4Abo1GXUnjrmLA55vhHG2DYCh6 3RNpW86RtRfwAqhf+O+zn1uSyBcFa2T7pfO2qyu1MwEZdpZ6eAKi36N7pRKj5Da9ZTDA Y9asSF8GzQphNYLAZfl/vPcHYlZppDsfpMpteKm3OzB/12XQa3oYm1S817kKbXBnfACk avKMdUu+25VBPgrWM3hSyXGBWDzbk8NsL595x+k/nuj4cpiDJODAgdQ9MTI1azXicD/3 xpGg== X-Gm-Message-State: APjAAAUnatvQ/xRqlCiWco5ngxNMIpwdDAiAZS3xveVgKJa1ZVmbQPaY XUjanz9DGrTNh4MHer+JKHQ= X-Google-Smtp-Source: APXvYqxkmwm8HYzroVBYOTrzQiJ2VWw+/UnCk4GK9eBTIIqLoX8iwmfeCjlji9FzaiCK4Cy6sNGtew== X-Received: by 2002:adf:ed0e:: with SMTP id a14mr15171502wro.259.1565244766283; Wed, 07 Aug 2019 23:12:46 -0700 (PDT) Received: from [192.168.8.147] (72.163.185.81.rev.sfr.net. [81.185.163.72]) by smtp.gmail.com with ESMTPSA id b203sm2250184wmd.41.2019.08.07.23.12.45 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Aug 2019 23:12:45 -0700 (PDT) Subject: Re: [PATCH v2 1/2] tcp: add new tcp_mtu_probe_floor sysctl To: Josh Hunt , netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, ncardwell@google.com References: <1565221950-1376-1-git-send-email-johunt@akamai.com> From: Eric Dumazet Message-ID: Date: Thu, 8 Aug 2019 08:12:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <1565221950-1376-1-git-send-email-johunt@akamai.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 8/8/19 1:52 AM, Josh Hunt wrote: > The current implementation of TCP MTU probing can considerably > underestimate the MTU on lossy connections allowing the MSS to get down to > 48. We have found that in almost all of these cases on our networks these > paths can handle much larger MTUs meaning the connections are being > artificially limited. Even though TCP MTU probing can raise the MSS back up > we have seen this not to be the case causing connections to be "stuck" with > an MSS of 48 when heavy loss is present. > > Prior to pushing out this change we could not keep TCP MTU probing enabled > b/c of the above reasons. Now with a reasonble floor set we've had it > enabled for the past 6 months. I am still sad to see you do not share what is a reasonable value and let everybody guess. It seems to be a top-secret value. > > The new sysctl will still default to TCP_MIN_SND_MSS (48), but gives > administrators the ability to control the floor of MSS probing. > > Signed-off-by: Josh Hunt Signed-off-by: Eric Dumazet