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 ws5-mx01.kavi.com (ws5-mx01.kavi.com [34.193.7.191]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2E33AC7EE23 for ; Wed, 24 May 2023 06:07:24 +0000 (UTC) Received: from lists.oasis-open.org (oasis.ws5.connectedcommunity.org [10.110.1.242]) by ws5-mx01.kavi.com (Postfix) with ESMTP id 8DE5A41F09 for ; Wed, 24 May 2023 06:07:23 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 7D8DC98641F for ; Wed, 24 May 2023 06:07:23 +0000 (UTC) Received: from host09.ws5.connectedcommunity.org (host09.ws5.connectedcommunity.org [10.110.1.97]) by lists.oasis-open.org (Postfix) with QMQP id 740DA986407; Wed, 24 May 2023 06:07:23 +0000 (UTC) Mailing-List: contact virtio-dev-help@lists.oasis-open.org; run by ezmlm List-ID: Sender: Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 610FC9862F6 for ; Wed, 24 May 2023 06:07:21 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: Cqa9-qkMMeqx00oRD6rQNg-1 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1684908438; x=1687500438; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=OJ6EvxvePm0YyvE2lzyaV2EoQdlp1UzZNmEnvDbUqRs=; b=in38VIvXJ3/ZBPSdbwQTwbamsCb9fIcKednejBMsmVZ0FUIvWsnqgk4CqazfkMFj8G VguPA13z9A//rrUGvLT0bbiBFZ5DP3BK5nqsf/kAgBU5lQvOl3KQenXWA5M/HpNT3a/6 ddRnjL17qr1a0N046H4uyrnBTspnr4NR/UKamNNkpbFYwFgeyAS1oW7UnrOXtYSQL8Nk xjAMIafveNa/aNLZbCPJJI4VF9jCwO4nS1tJAXlAEACqU92dLurBo2cRofyLK6fdDqX2 H1PYri03MRGgZsL04MSw7e9FconoUbPAwqX+KAfUPUi026l9GCwjP59fF2ARx5ehGogK Em8Q== X-Gm-Message-State: AC+VfDxan/5dSv1ZHvv3yCAv+PqvyeKRkfKiQPWSiuWDM7khPbmEUWPD XQBAhmEIO8FCXy3f/dmYaervn+Lf7ETpFpIkK8h9hJLjk49L0f8nZwZW5xHN4jAxXc0l9fK4lx6 REJqJSdrVCK5hS76bvSxXq/0XGsmG X-Received: by 2002:a05:600c:ac6:b0:3f1:8c5f:dfc5 with SMTP id c6-20020a05600c0ac600b003f18c5fdfc5mr11929579wmr.39.1684908437907; Tue, 23 May 2023 23:07:17 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ6isFdOLu5WPDq+FEXS+0cSs9D9Q3Da1udTru3G7PxcUhi4xWYMfyR6zdH6dojjh7aqBKakmQ== X-Received: by 2002:a05:600c:ac6:b0:3f1:8c5f:dfc5 with SMTP id c6-20020a05600c0ac600b003f18c5fdfc5mr11929563wmr.39.1684908437579; Tue, 23 May 2023 23:07:17 -0700 (PDT) Date: Wed, 24 May 2023 02:07:14 -0400 From: "Michael S. Tsirkin" To: Heng Qi Cc: virtio-dev@lists.oasis-open.org, virtio-comment@lists.oasis-open.org, Jason Wang , Parav Pandit , Xuan Zhuo Message-ID: <20230524020227-mutt-send-email-mst@kernel.org> References: <20230522121200.40939-1-hengqi@linux.alibaba.com> <20230522150743-mutt-send-email-mst@kernel.org> <20230523024118.GA23504@h68b04307.sqa.eu95> <20230523024057-mutt-send-email-mst@kernel.org> <20230523091820.GC23504@h68b04307.sqa.eu95> <20230523092237-mutt-send-email-mst@kernel.org> <20230523135144.GD23504@h68b04307.sqa.eu95> MIME-Version: 1.0 In-Reply-To: <20230523135144.GD23504@h68b04307.sqa.eu95> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [virtio-dev] Re: [virtio-comment] Re: [virtio-dev] Re: [Proposal] Relationship between XDP and rx-csum in virtio-net On Tue, May 23, 2023 at 09:51:44PM +0800, Heng Qi wrote: > On Tue, May 23, 2023 at 09:30:28AM -0400, Michael S. Tsirkin wrote: > > On Tue, May 23, 2023 at 05:18:20PM +0800, Heng Qi wrote: > > > On Tue, May 23, 2023 at 03:15:37AM -0400, Michael S. Tsirkin wrote: > > > > On Tue, May 23, 2023 at 10:41:18AM +0800, Heng Qi wrote: > > > > > On Mon, May 22, 2023 at 03:10:05PM -0400, Michael S. Tsirkin wrote: > > > > > > On Mon, May 22, 2023 at 08:12:00PM +0800, Heng Qi wrote: > > > > > > > 1) Add a feature bit to the virtio specification to tell the sender that a fully > > > > > > > csumed packet must be sent. > > > > > > > > > > > > Who is the sender in this picture? The driver? > > > > > > > > > > The device or the driver. > > > > > > > > > > When the device is hw, the sender is more likely to be a device. > > > > > When the device is sw, the sender can be a device or a driver. > > > > > > > > > > But in general, this feature is inclined to constrain the behavior of the device and > > > > > the driver from the receiving side. > > > > > > > > Based on above I am guessing you are talking about driver getting > > > > packets from device, I wish you used terms from virtio spec. > > > > > > Yes, I'm going to use the terminology of the virtio spec. > > > > > > > > > > > > For example: > > > > > VIRTIO_NET_F_UNNECESSARY_CSUM : The driver tells the device that you must send me a fully csumed packet. > > > > > > > > > > Then the specific implementation can be > > > > > > > > > > (1) the sender sends a fully csumed packet; > > > > > (2) the receiver receives a CHECKSUM_PARTIAL packet, and the device helps calculate the fully csum > > > > > (because the two parties in the communication are located on the same host, the packet is trusted.). > > > > > > > > > > In summary, if VIRTIO_NET_F_UNNECESSARY_CSUM is negotiated, the driver will no longer receive any packets marked CHECKSUM_PARTIAL. > > > > > > > > > > Thanks. > > > > > > > > This is what clearing VIRTIO_NET_F_GUEST_CSUM does. > > > > > > Yes, but with VIRTIO_NET_F_GUEST_CSUM cleared, although the device can > > > receive a fully checksummed packet, we can no longer enjoy > > > the device's ability to validate the packet checksum. That is, the value > > > of \field{flags} in the virtio_net_hdr structure is set to 0, which means > > > that the packet received by the driver will not be marked as > > > VIRTIO_NET_HDR_F_DATA_VALID. > > > > > > So, we need a feature bit (let's say VIRTIO_NET_F_UNNECESSARY_CSUM). > > > If VIRTIO_NET_F_UNNECESSARY_CSUM is negotiated, the device must give the > > > driver a fully checksummed packet, and the packet is validated by the > > > device with \field{flags} set to VIRTIO_NET_HDR_F_DATA_VALID. > > > > > > > > > > > I feel you are trying to say that clearing VIRTIO_NET_F_GUEST_CSUM > > > > disables all offloads but you want to keep some of them? > > > > > > > > > > No, what I mean is that a feature VIRTIO_NET_F_UNNECESSARY_CSUM is needed > > > in addition to VIRTIO_NET_F_GUEST_CSUM, if both features are negotiated, > > > then the driver may always receive packets marked as > > > VIRTIO_NET_HDR_F_DATA_VALID, which means that we can now load XDP at the > > > same time. > > > > Makes no sense to me. VIRTIO_NET_F_GUEST_CSUM set already allows > > VIRTIO_NET_HDR_F_DATA_VALID: > > We need to focus on what happens when the XDP program is loaded: > > The current virtio-net needs to turn off the VIRTIO_NET_F_GUEST_CSUM > feature when loading XDP. The main reason for doing this is because > VIRTIO_NET_F_GUEST_CSUM allows to receive packets marked as > VIRTIO_NET_HDR_F_NEEDS_CSUM. Such packets are not compatible with > XDP programs, because we cannot guarantee that the csum_{start, offset} > fields are correct after XDP modifies the packets. What do you want the device to do with these packets? Just clear VIRTIO_NET_HDR_F_NEEDS_CSUM? Then ... why don't you have the driver clear that bit? > So in order for the driver to continue to enjoy the device's ability to > validate packets while XDP is loaded, we need a new feature to tell the > device not to deliver packets marked as VIRTIO_NET_HDR_F_NEEDS_CSUM (in > other words, the device can only deliver packets marked as > VIRTIO_NET_HDR_F_DATA_VALID). > > Thanks. > > \item If the VIRTIO_NET_F_GUEST_CSUM feature was negotiated, the > > VIRTIO_NET_HDR_F_NEEDS_CSUM bit in \field{flags} can be > > set: if so, the packet checksum at offset \field{csum_offset} > > from \field{csum_start} and any preceding checksums > > have been validated. The checksum on the packet is incomplete and > > if bit VIRTIO_NET_HDR_F_RSC_INFO is not set in \field{flags}, > > then \field{csum_start} and \field{csum_offset} indicate how to calculate it > > (see Packet Transmission point 1). > > > > Did you maybe mean if either feature is negotiated? > > > > > > > > > > Again please use virtio terminology not Linux. to help you out, > > > > in current linux, VIRTIO_NET_HDR_F_NEEDS_CSUM and VIRTIO_NET_HDR_F_DATA_VALID > > > > will set CHECKSUM_PARTIAL and CHECKSUM_UNNECESSARY respectively. > > > > > > > > > > Sure. Will do as you suggested. > > > > > > Thanks. > > > > > > > > > > > -- > > > > MST > > > > > > > > > > > > --------------------------------------------------------------------- > > > > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > > > > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org > > > > > > This publicly archived list offers a means to provide input to the > > OASIS Virtual I/O Device (VIRTIO) TC. > > > > In order to verify user consent to the Feedback License terms and > > to minimize spam in the list archive, subscription is required > > before posting. > > > > Subscribe: virtio-comment-subscribe@lists.oasis-open.org > > Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org > > List help: virtio-comment-help@lists.oasis-open.org > > List archive: https://lists.oasis-open.org/archives/virtio-comment/ > > Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf > > List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lists > > Committee: https://www.oasis-open.org/committees/virtio/ > > Join OASIS: https://www.oasis-open.org/join/ --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org