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=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 014B8C433DB for ; Fri, 12 Mar 2021 06:25:24 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7222364F76 for ; Fri, 12 Mar 2021 06:25:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7222364F76 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:44386 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lKbEg-0003zz-EX for qemu-devel@archiver.kernel.org; Fri, 12 Mar 2021 01:25:22 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:34020) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lKbCb-0002EJ-7A for qemu-devel@nongnu.org; Fri, 12 Mar 2021 01:23:13 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:44280) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lKbCZ-0001HM-AS for qemu-devel@nongnu.org; Fri, 12 Mar 2021 01:23:12 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615530190; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=j6YV1/V89fSTJ9phlXpvTyC0V9+WxasCflts+Ckkp0k=; b=SaQ5JP2arHpx5oibW3NyEKB7ZJ6liEW4azF9OgI7YXBHDwMb2lFpc/Q1VgciRIDtZJxb7J zpDDpm8B5IrHxmQyeU3xnnAe9ZtdvcYcB3Wg6lSWNiWnKZjNH0MMvaoaAtuy6EcAAsNSVI vSLWaIonDLTs3Anpx28WncBgiHOYZxI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-139-CMlvpCcNNoe-6tVdOtwqXQ-1; Fri, 12 Mar 2021 01:23:07 -0500 X-MC-Unique: CMlvpCcNNoe-6tVdOtwqXQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8DC41107ACCA; Fri, 12 Mar 2021 06:23:05 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-33.pek2.redhat.com [10.72.13.33]) by smtp.corp.redhat.com (Postfix) with ESMTP id 349D25D9F2; Fri, 12 Mar 2021 06:22:56 +0000 (UTC) Subject: Re: [RFC PATCH v3 02/10] net: Pad short frames to minimum size before send from SLiRP/TAP To: Bin Meng , Peter Maydell References: <20210303191205.1656980-1-philmd@redhat.com> <20210303191205.1656980-3-philmd@redhat.com> <36123f35-06ab-d0da-37d2-6f8324e7f582@redhat.com> From: Jason Wang Message-ID: <4cc1bcb9-2288-ac03-4a5f-a1ebad4d34ef@redhat.com> Date: Fri, 12 Mar 2021 14:22:54 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB Received-SPF: pass client-ip=216.205.24.124; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.25, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Dmitry Fleytman , "Michael S. Tsirkin" , Bin Meng , Richard Henderson , QEMU Developers , Stefan Hajnoczi , "Edgar E. Iglesias" , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2021/3/11 6:27 下午, Bin Meng wrote: > On Thu, Mar 11, 2021 at 6:22 PM Peter Maydell wrote: >> On Thu, 11 Mar 2021 at 09:58, Bin Meng wrote: >>> On Thu, Mar 11, 2021 at 5:43 PM Peter Maydell wrote: >>>> On Thu, 11 Mar 2021 at 03:01, Jason Wang wrote: >>>>> And after a discussion 10 years ago [1]. Michael (cced) seems to want to >>>>> keep the padding logic in the NIC itself (probably with a generic helper >>>>> in the core). Since 1) the padding is only required for ethernet 2) >>>>> virito-net doesn't need that (it can pass incomplete packet by design). >>>> Like I said, we need to decide; either: >>>> >>>> (1) we do want to support short packets in the net core: >>>> every sender needs to either pad, or to have some flag to say >>>> "my implementation can't pad, please can the net core do it for me", >>>> unless they are deliberately sending a short packet. Every >>>> receiver needs to be able to cope with short packets, at least >>>> in the sense of not crashing (they should report them as a rx >>>> error if they have that kind of error reporting status register). >>>> I think we have mostly implemented our NIC models this way. >>>> >>>> (2) we simply don't support short packets in the net core: >>>> nobody (not NICs, not network backends) needs to pad, because >>>> they can rely on the core to do it. Some existing senders and >>>> receivers may have now-dead code to do their own padding which >>>> could be removed. >>>> >>>> MST is advocating for (1) in that old thread. That's a coherent >>>> position. >>> But it's a wrong approach. As Edgar and Stefan also said in the old >>> discussion thread, padding in the RX is wrong as real world NICs don't >>> do this. >> Neither option (1) nor option (2) involve padding in RX. > Correct. What I referred to is the current approach used in many NIC > modes, which is wrong, and we have to correct this. > >> Option (1) is: >> * no NIC implementation pads on TX, except as defined >> by whatever NIC-specific config registers or h/w behaviour >> might require (ie if the guest wants to send a short packet >> it can do that) >> * non-NIC sources like slirp need to pad on TX unless they're >> deliberately trying to send a short packet >> * all receivers of packets need to cope with being given a >> short packet; this is usually going to mean "flag it to the >> guest as an RX error", but exact behaviour is NIC-dependent >> > My patch series in RFC v2/v3 does almost exactly this option (1), > except "flag it to the guest as an RX error". Is it? You did it at net core instead of netdevs if I read the code correctly. > >> Option (2) is: >> * the net core code pads any packet that goes through it >> * no NIC implementation needs to pad on TX (it is harmless if they do) >> * non-NIC sources don't need to pad on TX >> * no receivers of packets need to cope with being given short packets >> >> Option 1 is what the real world does. Option 2 is a simplification >> which throws away the ability to emulate handling of short packets, >> in exchange for not having to sort out senders like slirp and not >> having to be so careful about short-packet handling in NIC models. >> >> If MST is correct that some use cases require short-packet support, >> then we need to go for option 1, I think. For NIC RX, I wonder whether we can introduce a boolean to whether it requries padding. And then the netdevs can only do the padding when it's required. E.g virito-net doesn't need padding. Thanks > Regards, > Bin >