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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 BCA7BC432C0 for ; Sat, 23 Nov 2019 21:54:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E4A5206D4 for ; Sat, 23 Nov 2019 21:54:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="iSsLcMpI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726836AbfKWVyb (ORCPT ); Sat, 23 Nov 2019 16:54:31 -0500 Received: from mail-ed1-f66.google.com ([209.85.208.66]:35739 "EHLO mail-ed1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726735AbfKWVyb (ORCPT ); Sat, 23 Nov 2019 16:54:31 -0500 Received: by mail-ed1-f66.google.com with SMTP id r16so9147714edq.2 for ; Sat, 23 Nov 2019 13:54:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Nx+NTZhTCLYxgGLVamdv8eGkC8vIdDFveuRrdSyH/ro=; b=iSsLcMpIzth+XU4BIKj5lKPuDQi2jds1bmuwMblfRurbBQCg1DcGmY5wXbizTK4pbT lcpUG+q1Wu1nsMbL4oXL3LImSBFR4vQbIEmQTE81YlOUkoooBNind8bDo5GbKl35i28r m+DCqCMGCeBWHiCAqrKj2Rdr+S+cUpAPHQKEijHaMsNl3H9h7UV1uAqocH9m69ACoC6P q5d+zymRr4Tc5vBCYr6iVvEmdo8PWcbiWyJA/lmA/ydihNNVbyPVaJFwT9nfY0WTAIrr kxOd491zvpHLhFvhUoVbTC3ZtrgQNyQLckx81WWqp/Vd8aNi+xwfcdzuTRqENlhpxohP XF+w== 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; bh=Nx+NTZhTCLYxgGLVamdv8eGkC8vIdDFveuRrdSyH/ro=; b=EOqggJX2OM1Ft+wtYJ+6IKKEmhw8Y/0tXn0o3xuLImV0COka2TexMSfFwQPnBQxwpr hCHYatquoEEO6wJsmE5owl5An7H5KJB4EV3+PmB2h39V6e4HAPb8EzXi0WEH14+jVhoH yuXxiW7/xT0kToj/wnY3fj6mLBMZ8rtqfglr+DSF8aG4PROB/tjsbsXvv1xY9m2tOyjt oVjX+DEPI70e0YL3DMUXITxZMI8L4TRJm1ZIWWlrGqixfkA6rG60t/OAtXBwqvzmrXw9 0fU9rf/fQDKiKohfPubJcFhZAXDOxF32nmoNGHESXqL5EJKS6rqja1rnBPHIyZExVXOm e9FQ== X-Gm-Message-State: APjAAAVdVk91KUvHRHUWQ3QbxcHS/PV1wSWWpTytA6kC/LiIvyHDYV3k Nj/KH4bDEohn9Qf4ZuZg9F6ETbH1PecLy2Tce8o= X-Google-Smtp-Source: APXvYqxEyLw9q8U/LHvi+gJz8lTFHBjjEWE7Fcg1fuaIGkNdjwlVkdsO9jpe39JpFy0skkXSNRwf6H/nZ1Y+FTw4Me8= X-Received: by 2002:a17:906:4910:: with SMTP id b16mr28801172ejq.133.1574546068075; Sat, 23 Nov 2019 13:54:28 -0800 (PST) MIME-Version: 1.0 References: <20191123194844.9508-1-olteanv@gmail.com> <20191123194844.9508-2-olteanv@gmail.com> <329f394b-9e6c-d3b0-dc3d-5e3707fa8dd7@gmail.com> <9f344984-ef0c-fc57-d396-48d4c77e1954@gmail.com> In-Reply-To: From: Vladimir Oltean Date: Sat, 23 Nov 2019 23:54:17 +0200 Message-ID: Subject: Re: [PATCH net-next 1/3] net: dsa: Configure the MTU for switch ports To: Florian Fainelli Cc: Andrew Lunn , Vivien Didelot , "David S. Miller" , Jakub Kicinski , netdev Content-Type: text/plain; charset="UTF-8" Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sat, 23 Nov 2019 at 23:47, Florian Fainelli wrote: > On 11/23/2019 1:29 PM, Vladimir Oltean wrote: > > On Sat, 23 Nov 2019 at 23:14, Florian Fainelli wrote: > >> On 11/23/2019 12:46 PM, Vladimir Oltean wrote: [snip] > >>>> Another thing that I had not gotten around testing was making sure that > >>>> when a slave_dev gets enslaved as a bridge port member, that bridge MTU > >>>> normalization would kick in and make sure that if you have say: port 0 > >>>> configured with MTU 1500 and port 1 configured with MTU 9000, the bridge > >>>> would normalize to MTU 1500 as you would expect. > >>>> > >>> > >>> Nope, that doesn't happen by default, at least in my implementation. > >>> Is there code in the bridge core for it? > >> > >> net/bridge/br_if.c::br_mtu_auto_adjust() takes care of adjusting the > >> bridge master device's MTU based on the minimum MTU of all ports within > >> the bridge, but what it seems to be missing is ensuring that if bridge > >> ports are enslaved, and those bridge ports happen to be part of the same > >> switch id (similar decision path to setting skb->fwd_offload_mark), then > >> the bridge port's MTU should also be auto adjusted. mlxsw also supports > >> changing the MTU, so I am surprised this is not something they fixed > >> already. > >> > > > > But then how would you even change a bridged interface's MTU? Delete > > bridge, change MTU of all ports to same value, create bridge again? > > I am afraid so, given that the NETDEV_CHANGEMTU even for which > br_device_event() listens to and processes with br_mtu_auto_adjust() > would lead to selecting the lowest MTU again. Unfortunately, I don't > really see a way to solve that other than walk all ports (which could be > any network device driver) and ask them if they support the new MTU of > that other port, and if so, commit, else rollback. Do you see another way? > -- > Florian Something like that would be preferable. I think it would be frustrating for the bridge to restore the old MTU right after you change it. I have no idea how hard it would be to prevent the bridge from doing this. I'll poke it with a stick and see what happens. -Vladimir