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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5C4D4C433F5 for ; Fri, 4 Mar 2022 04:33:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235041AbiCDEec (ORCPT ); Thu, 3 Mar 2022 23:34:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57586 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232508AbiCDEeb (ORCPT ); Thu, 3 Mar 2022 23:34:31 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 251B07E09B for ; Thu, 3 Mar 2022 20:33:44 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B892B61B2D for ; Fri, 4 Mar 2022 04:33:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 517BEC340E9; Fri, 4 Mar 2022 04:33:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1646368423; bh=ms5gbFrkn1tBhmSYGgFLRPeodsPSp/ox0qL8N7ANDOQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ur3g5y3/o2S8eBXZKR6Ml/uUAVstB53Fasy0u5ltzwoSIwvx2jRb7LbTbpfk9mkk5 ZKRatQYgxt1nuZe9pEyrj9Mua9r2fETZbGsuq9P0P66rl0EAbw7J/6ljwMAqU8xPvq SpN9X66xa91Q3U1i3CQbnEuMkzfWYm9GjXw477khrrZ8KxPDcAXD2eb7bxBw6czu4t blQIqKK7qOMg4nCegKoQ+kYofejHdwymbj9qvKjLxQ/IeVm1eEY4f8+z4q8bHNlqqG PVuaYyzJD0i3zfMPN69jOadOARN2FavsfzotZbqTz43kE1gDtHjQ8lKT6+m6vAMOO6 MatP+mKM3ERXg== Message-ID: <726720e6-cd28-646c-1ba3-576a258ae02e@kernel.org> Date: Thu, 3 Mar 2022 21:33:39 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH v2 net-next 08/14] ipv6: Add hop-by-hop header to jumbograms in ip6_output Content-Language: en-US To: Eric Dumazet , "David S . Miller" , Jakub Kicinski Cc: netdev , Eric Dumazet , Coco Li , Alexander Duyck References: <20220303181607.1094358-1-eric.dumazet@gmail.com> <20220303181607.1094358-9-eric.dumazet@gmail.com> From: David Ahern In-Reply-To: <20220303181607.1094358-9-eric.dumazet@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 3/3/22 11:16 AM, Eric Dumazet wrote: > From: Coco Li > > Instead of simply forcing a 0 payload_len in IPv6 header, > implement RFC 2675 and insert a custom extension header. > > Note that only TCP stack is currently potentially generating > jumbograms, and that this extension header is purely local, > it wont be sent on a physical link. > > This is needed so that packet capture (tcpdump and friends) > can properly dissect these large packets. > I am fairly certain I know how you are going to respond, but I will ask this anyways :-) : The networking stack as it stands today does not care that skb->len > 64kB and nothing stops a driver from setting max gso size to be > 64kB. Sure, packet socket apps (tcpdump) get confused but if the h/w supports the larger packet size it just works. The jumbogram header is getting adding at the L3/IPv6 layer and then removed by the drivers before pushing to hardware. So, the only benefit of the push and pop of the jumbogram header is for packet sockets and tc/ebpf programs - assuming those programs understand the header (tcpdump (libpcap?) yes, random packet socket program maybe not). Yes, it is a standard header so apps have a chance to understand the larger packet size, but what is the likelihood that random apps or even ebpf programs will understand it? Alternative solutions to the packet socket (ebpf programs have access to skb->len) problem would allow IPv4 to join the Big TCP party. I am wondering how feasible an alternative solution is to get large packet sizes across the board with less overhead and changes.