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 A82B1C38A2D for ; Mon, 24 Oct 2022 21:20:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234038AbiJXVT5 (ORCPT ); Mon, 24 Oct 2022 17:19:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50560 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235412AbiJXVTe (ORCPT ); Mon, 24 Oct 2022 17:19:34 -0400 Received: from mslow1.mail.gandi.net (mslow1.mail.gandi.net [IPv6:2001:4b98:dc4:8::240]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7D121C96CD; Mon, 24 Oct 2022 12:25:46 -0700 (PDT) Received: from relay2-d.mail.gandi.net (unknown [IPv6:2001:4b98:dc4:8::222]) by mslow1.mail.gandi.net (Postfix) with ESMTP id 08002C16B0; Mon, 24 Oct 2022 15:40:51 +0000 (UTC) Received: (Authenticated sender: i.maximets@ovn.org) by mail.gandi.net (Postfix) with ESMTPSA id 9001540008; Mon, 24 Oct 2022 15:39:14 +0000 (UTC) Message-ID: <1ac55929-4399-484c-e3ee-1a04f8e90046@ovn.org> Date: Mon, 24 Oct 2022 17:39:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.1 Cc: i.maximets@ovn.org, netdev@vger.kernel.org, "David S. Miller" , Eric Dumazet , Paolo Abeni , linux-kernel@vger.kernel.org Content-Language: en-US To: nicolas.dichtel@6wind.com, Jakub Kicinski References: <20221021114921.3705550-1-i.maximets@ovn.org> <20221021090756.0ffa65ee@kernel.org> <5af190a8-ac35-82a6-b099-e9a817757676@6wind.com> From: Ilya Maximets Subject: Re: [RFE net-next] net: tun: 1000x speed up In-Reply-To: <5af190a8-ac35-82a6-b099-e9a817757676@6wind.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/24/22 14:27, Nicolas Dichtel wrote: > Le 24/10/2022 à 13:56, Ilya Maximets a écrit : >> On 10/24/22 11:44, Nicolas Dichtel wrote: >>> Le 21/10/2022 à 18:07, Jakub Kicinski a écrit : >>>> On Fri, 21 Oct 2022 13:49:21 +0200 Ilya Maximets wrote: >>>>> Bump the advertised speed to at least match the veth. 10Gbps also >>>>> seems like a more or less fair assumption these days, even though >>>>> CPUs can do more. Alternative might be to explicitly report UNKNOWN >>>>> and let the application/user decide on a right value for them. >>>> >>>> UNKOWN would seem more appropriate but at this point someone may depend >>>> on the speed being populated so it could cause regressions, I fear :S >>> If it is put in a bonding, it may cause some trouble. Maybe worth than >>> advertising 10M. >> >> My thoughts were that changing the number should have a minimal impact >> while changing it to not report any number may cause some issues in >> applications that doesn't expect that for some reason (not having a >> fallback in case reported speed is unknown isn't great, and the argument >> can be made that applications should check that, but it's hard to tell >> for every application if they actually do that today). >> >> Bonding is also a good point indeed, since it's even in-kernel user. >> >> >> The speed bump doesn't solve the problem per se. It kind of postpones >> the decision, since we will run into the same issue eventually again. >> That's why I wanted to discuss that first. >> >> Though I think that at least unification across virtual devices (tun and >> veth) should be a step in a right direction. > Just to make it clear, I'm not against aligning speed with veth, I'm only > against reporting UNKNOWN. Ack. Thanks for the clarification! > >> >>> >>> Note that this value could be configured with ethtool: >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4e24f2dd516ed >> >> This is interesting, but it's a bit hard to manage, because in order >> to make a decision to bump the speed, application should already know >> that this is a tun/tap device. So, there has to be a special case > But this should be done by the application which creates this tun interface. Not > by the application that uses this information. > >> implemented in the code that detects the driver and changes the speed >> (this is about application that is using the interface, but didn't >> create it), but if we already know the driver, then it doesn't make >> sense to actually change the speed in many cases as application can >> already act accordingly. >> >> Also, the application may not have permissions to do that (I didn't >> check the requirements, but my guess would be at least CAP_NET_ADMIN?). > Sure, but the one who creates it, has the right to configure it correctly. It's > part of the configuration of the interface. I mostly agree with that, but that still means changing userspace applications. I'm pretty sure very little number of applications, if any at all, do that today. > > Setting an higher default speed seems to be a workaround to fix an incorrect > configuration. And as you said, it will probably be wrong again in a few years ;-) Yep. Workarounds do exist today. For example, if you specify max-rate in QoS configuration for OVS, it will not use the link speed as a reference at all. I'm just not sure if replacing one workaround with another workaround is a good option. Especially because that will require changing userspace applications and the problem itself is kind of artificial. > >> >> For the human user it's still one extra configuration step that they >> need to remember to perform. > I don't buy this argument. There are already several steps: creating and > configuring an interface requires more than one command. Muscle memory, I guess. :) But yes, might not be a huge deal for human users, I agree. It's more of a concern for multi-layer systems where actual interfaces are created somewhere deep inside the software stack and actual humans don't really perform these commands by hands. Best regards, Ilya Maximets.