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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no 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 51DC7C433FF for ; Fri, 9 Aug 2019 19:59:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3115720C01 for ; Fri, 9 Aug 2019 19:59:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727278AbfHIT7D (ORCPT ); Fri, 9 Aug 2019 15:59:03 -0400 Received: from shards.monkeyblade.net ([23.128.96.9]:37252 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726022AbfHIT7C (ORCPT ); Fri, 9 Aug 2019 15:59:02 -0400 Received: from localhost (unknown [IPv6:2601:601:9f80:35cd::d71]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 4763C144A3A68; Fri, 9 Aug 2019 12:59:02 -0700 (PDT) Date: Fri, 09 Aug 2019 12:59:01 -0700 (PDT) Message-Id: <20190809.125901.428600986132688806.davem@davemloft.net> To: johunt@akamai.com Cc: netdev@vger.kernel.org, edumazet@google.com, ncardwell@google.com Subject: Re: [PATCH v2 1/2] tcp: add new tcp_mtu_probe_floor sysctl From: David Miller In-Reply-To: <1565221950-1376-1-git-send-email-johunt@akamai.com> References: <1565221950-1376-1-git-send-email-johunt@akamai.com> X-Mailer: Mew version 6.8 on Emacs 26.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Fri, 09 Aug 2019 12:59:02 -0700 (PDT) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Josh Hunt Date: Wed, 7 Aug 2019 19:52:29 -0400 > 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. > > 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 Applied.