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 59106C433F5 for ; Tue, 29 Mar 2022 04:34:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232096AbiC2Efp (ORCPT ); Tue, 29 Mar 2022 00:35:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39188 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231463AbiC2Efj (ORCPT ); Tue, 29 Mar 2022 00:35:39 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EA08164F9; Mon, 28 Mar 2022 21:33:56 -0700 (PDT) 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 3F70F613EF; Tue, 29 Mar 2022 04:33:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C7621C2BBE4; Tue, 29 Mar 2022 04:33:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1648528435; bh=5dIB0sxX2lYZvf6q2/JasfE5c9SjoX2u6XVBPnKxdEE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=tTUVZy56vvtMa/80ckzceNeLXsipjdpOiYLG5fITqgQ3K11etN6s4by/QIvF9syPp FOW/sA3pq9+VoOfdXnlpx/+d5brcX4a4z4xmk0RQ4Sm2Hnon0ns61vCT/gD30jqZsE KMpeM4EdAf/WMXC6oOI+r9Ij5P+hbKv+kKUCloyoYS4Embeb5qJCDzY06woXIuPZdD DWSRmY6207Gpegb2jdRBex4HVqJcbgY4k4o30SHIi3849cJ2OvfVROguiO+owU3r5U 2BQwPcjnOk+ITrZ8ku/sp2rUH6s6+fSdaf3LgTgOQUX8pRGyVx93VwZQ6voKzatxrU HoqRTrUXlMn+g== Date: Mon, 28 Mar 2022 21:33:53 -0700 From: Jakub Kicinski To: Mingbao Sun Cc: Sagi Grimberg , Keith Busch , Jens Axboe , Christoph Hellwig , Chaitanya Kulkarni , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, Eric Dumazet , "David S . Miller" , Hideaki YOSHIFUJI , David Ahern , netdev@vger.kernel.org, tyler.sun@dell.com, ping.gan@dell.com, yanxiu.cai@dell.com, libin.zhang@dell.com, ao.sun@dell.com Subject: Re: [PATCH v2 2/3] nvme-tcp: support specifying the congestion-control Message-ID: <20220328213353.4aca75bd@kernel.org> In-Reply-To: <20220329104806.00000126@tom.com> References: <20220311103414.8255-1-sunmingbao@tom.com> <20220311103414.8255-2-sunmingbao@tom.com> <7121e4be-0e25-dd5f-9d29-0fb02cdbe8de@grimberg.me> <20220325201123.00002f28@tom.com> <20220329104806.00000126@tom.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 29 Mar 2022 10:48:06 +0800 Mingbao Sun wrote: > A server in a data-center with the following 2 NICs: >=20 > - NIC_fron-end, for interacting with clients through WAN > (high latency, ms-level) >=20 > - NIC_back-end, for interacting with NVMe/TCP target through LAN > (low latency, ECN-enabled, ideal for dctcp) >=20 > This server interacts with clients (handling requests) via the fron-end > network and accesses the NVMe/TCP storage via the back-end network. > This is a normal use case, right? Well, if you have clearly separated networks you can set the congestion control algorithm per route, right? man ip-route, search congctl. > For the client devices, we can=E2=80=99t determine their congestion-contr= ol. > But normally it=E2=80=99s cubic by default (per the CONFIG_DEFAULT_TCP_CO= NG). > So if we change the default congestion control on the server to dctcp > on behalf of the NVMe/TCP traffic of the LAN side, it could at the > same time change the congestion-control of the front-end sockets > to dctcp while the congestion-control of the client-side is cubic. > So this is an unexpected scenario. >=20 > In addition, distributed storage products like the following also have > the above problem: >=20 > - The product consists of a cluster of servers. >=20 > - Each server serves clients via its front-end NIC > (WAN, high latency). >=20 > - All servers interact with each other via NVMe/TCP via back-end NIC > (LAN, low latency, ECN-enabled, ideal for dctcp).