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 87112C4332F for ; Thu, 2 Nov 2023 06:50:41 +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 CDE292AC5A for ; Thu, 2 Nov 2023 06:50:40 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id B6516986BF3 for ; Thu, 2 Nov 2023 06:50:40 +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 983B9986BEB; Thu, 2 Nov 2023 06:50:40 +0000 (UTC) Mailing-List: contact virtio-comment-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 8E18D986BEC for ; Thu, 2 Nov 2023 06:50:14 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: oTbaYk4GMve9GgmHA41oEA-1 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1698907808; x=1699512608; h=in-reply-to:content-transfer-encoding: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=NUwp5DlZ3Nd9XTIFInAl4st30oJ/uMdda9twD1ApzcY=; b=sld1YNe2YeAsGczGfQnGyLCAVRNje0iwl3H+r+mFIFhDx5hC39oTRwnAN7VRlGlG0j JhJDa0rS5P3pJkBn53xUp2+iZ0nkTagFjoQCCaShprpWnhYJvg4GaPpdNYSGY6vZmT75 YB3q48fvZ9WqguJH/okQ++w4vvYstKkG+iC6CaPCqt9qXimoAM0gribLPWd5T++0dRxr glv/wh3k486yuBDMRZSNCd7RMliBbtpP/uiAqoekAffK8Q98WU6wxHwWob1NseQTdv7s EeahEEAJ3WivytWigYf8peUQr+RlssSRmSCPMp4wWlInsh9S4v/6qVGDaWto+Tr/Rqam qMjw== X-Gm-Message-State: AOJu0YyDyEkzftiexnnz5QGwmVAeFJxZgXA8FxR7mIH69POub8fN8++u XH3I111L34jROn2wjOh01z2cjdf2C8ChAAD1b5l77IAB86CzU0ya4YZ/PrWX6u+7LTGSshbo5Ls ILvIsIQAZ0WzxZt+mD/AamZnUlIDA+gozag== X-Received: by 2002:a2e:2e12:0:b0:2c5:582:fd8d with SMTP id u18-20020a2e2e12000000b002c50582fd8dmr14516546lju.30.1698907808543; Wed, 01 Nov 2023 23:50:08 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEDsvybm/3pYqPOK1m8o6Hsd/kZh9xka6kYI+0t83t1Dt8Rz96fb3JyvgmqStfExAcEPQas3A== X-Received: by 2002:a2e:2e12:0:b0:2c5:582:fd8d with SMTP id u18-20020a2e2e12000000b002c50582fd8dmr14516527lju.30.1698907808117; Wed, 01 Nov 2023 23:50:08 -0700 (PDT) Date: Thu, 2 Nov 2023 02:50:03 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: Heng Qi , virtio-comment@lists.oasis-open.org, Parav Pandit , Xuan Zhuo Message-ID: <20231102024425-mutt-send-email-mst@kernel.org> References: <20231027032707-mutt-send-email-mst@kernel.org> <79a89ece-f931-4a59-ac5c-25b60c4102a1@linux.alibaba.com> <20231101013634-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Subject: Re: [virtio-comment] [PATCH v2] virtio-net: support distinguishing between partial and full checksum On Thu, Nov 02, 2023 at 12:40:03PM +0800, Jason Wang wrote: > On Wed, Nov 1, 2023 at 1:37 PM Michael S. Tsirkin wrote: > > > > On Wed, Nov 01, 2023 at 12:16:23PM +0800, Jason Wang wrote: > > > On Sat, Oct 28, 2023 at 10:36 AM Heng Qi wrote: > > > > > > > > > > > > > > > > 在 2023/10/27 下午3:39, Michael S. Tsirkin 写道: > > > > > On Thu, Oct 19, 2023 at 02:17:20PM +0800, Heng Qi wrote: > > > > >> virtio-net works in a virtualized system and is somewhat different from > > > > >> physical nics. One of the differences is that to save virtio device > > > > >> resources, rx may receive packets with partial checksum. However, XDP may > > > > >> cause partially checksummed packets to be dropped. So XDP loading conflicts > > > > >> with the feature VIRTIO_NET_F_GUEST_CSUM. > > > > >> > > > > >> This patch lets the device to supply fully checksummed packets to the driver. > > > > >> Then XDP can coexist with VIRTIO_NET_F_GUEST_CSUM to enjoy the benefits of > > > > >> device verification checksum. > > > > >> > > > > >> In addition, implementation of some performant devices do not generate > > > > >> partially checksummed packets, but the standard driver still need to clear > > > > >> VIRTIO_NET_F_GUEST_CSUM when loading XDP. If these devices enable the > > > > >> full checksum offloading, then the driver can load XDP without clearing > > > > >> VIRTIO_NET_F_GUEST_CSUM. > > > > >> > > > > >> A new feature bit VIRTIO_NET_F_GUEST_FULL_CSUM is added to solve the above > > > > >> situation, which provides the driver with configurable receive full checksum > > > > >> offload. If the offload is enabled, then the device must supply fully > > > > >> checksummed packets to the driver. > > > > >> > > > > >> Use case example: > > > > >> If VIRTIO_NET_F_GUEST_FULL_CSUM is negotiated and receive full checksum > > > > >> offload is enabled, after XDP processes a packet with full checksum, the > > > > >> VIRTIO_NET_HDR_F_DATA_VALID bit is still retained, resulting in the stack > > > > >> not needing to validate the checksum again. This is useful for guests: > > > > >> 1. Bring the driver advantages such as cpu savings. > > > > >> 2. For devices that do not generate partially checksummed packets themselves, > > > > >> XDP can be loaded in the driver without modifying the hardware behavior. > > > > >> > > > > >> Several solutions have been discussed in the previous proposal[1]. > > > > >> After historical discussion, we have tried the method proposed by Jason[2], > > > > >> but some complex scenarios and challenges are difficult to deal with. > > > > >> We now return to the method suggested in [1]. > > > > >> > > > > >> [1] https://lists.oasis-open.org/archives/virtio-dev/202305/msg00291.html > > > > >> [2] https://lore.kernel.org/all/20230628030506.2213-1-hengqi@linux.alibaba.com/ > > > > >> > > > > >> Signed-off-by: Heng Qi > > > > >> Reviewed-by: Xuan Zhuo > > > > >> --- > > > > >> v1->v2: > > > > >> 1. Modify full checksum functionality as a configurable offload > > > > >> that is initially turned off. @Jason > > > > >> > > > > >> device-types/net/description.tex | 54 ++++++++++++++++++++++++++++---- > > > > >> 1 file changed, 48 insertions(+), 6 deletions(-) > > > > >> > > > > >> diff --git a/device-types/net/description.tex b/device-types/net/description.tex > > > > >> index 76585b0..3c34f27 100644 > > > > >> --- a/device-types/net/description.tex > > > > >> +++ b/device-types/net/description.tex > > > > >> @@ -88,6 +88,8 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits > > > > >> \item[VIRTIO_NET_F_CTRL_MAC_ADDR(23)] Set MAC address through control > > > > >> channel. > > > > >> > > > > >> +\item[VIRTIO_NET_F_GUEST_FULL_CSUM (50)] Driver handles packets with full checksum. > > > > >> + > > > > >> \item[VIRTIO_NET_F_HASH_TUNNEL(51)] Device supports inner header hash for encapsulated packets. > > > > >> > > > > >> \item[VIRTIO_NET_F_VQ_NOTF_COAL(52)] Device supports virtqueue notification coalescing. > > > > >> @@ -133,6 +135,7 @@ \subsubsection{Feature bit requirements}\label{sec:Device Types / Network Device > > > > >> \item[VIRTIO_NET_F_GUEST_UFO] Requires VIRTIO_NET_F_GUEST_CSUM. > > > > >> \item[VIRTIO_NET_F_GUEST_USO4] Requires VIRTIO_NET_F_GUEST_CSUM. > > > > >> \item[VIRTIO_NET_F_GUEST_USO6] Requires VIRTIO_NET_F_GUEST_CSUM. > > > > >> +\item[VIRTIO_NET_F_GUEST_FULL_CSUM] Requires VIRTIO_NET_F_GUEST_CSUM and VIRTIO_NET_F_CTRL_GUEST_OFFLOADS. > > > > >> > > > > >> \item[VIRTIO_NET_F_HOST_TSO4] Requires VIRTIO_NET_F_CSUM. > > > > >> \item[VIRTIO_NET_F_HOST_TSO6] Requires VIRTIO_NET_F_CSUM. > > > > > What about all of these: > > > > > > > > > > device-types/net/description.tex:\item[VIRTIO_NET_F_GUEST_TSO4] Requires VIRTIO_NET_F_GUEST_CSUM. > > > > > device-types/net/description.tex:\item[VIRTIO_NET_F_GUEST_TSO6] Requires VIRTIO_NET_F_GUEST_CSUM. > > > > > device-types/net/description.tex:\item[VIRTIO_NET_F_GUEST_UFO] Requires VIRTIO_NET_F_GUEST_CSUM. > > > > > device-types/net/description.tex:\item[VIRTIO_NET_F_GUEST_USO4] Requires VIRTIO_NET_F_GUEST_CSUM. > > > > > device-types/net/description.tex:\item[VIRTIO_NET_F_GUEST_USO6] Requires VIRTIO_NET_F_GUEST_CSUM. > > > > > > > > > > > > > > > > > > > > can TSO/UFO/USO work with VIRTIO_NET_F_GUEST_FULL_CSUM as opposed to VIRTIO_NET_F_GUEST_CSUM? > > > > > > > > Both GUEST_FULL_CSUM and GUEST_CSUM can work with GUEST_TSO/USO/UFO. > > > > > > Yes. For software devices I guess it will have a lot of performance > > > penalty. So it should be disabled by default anyhow. The idea is to > > > delay the csum as late as possible. > > > > But for hardware it's actually better. > > I can't think of a case where it might be better than XDP. Of course CHECKSUM_COMPLETE is better than CHECKSUM_PARTIAL if you can support it: you don't even need to look at csum_start + csum_offset. And the hardware doesn't need to parse L3/L4 headers to implement CHECKSUM_COMPLETE. > Most userspace doesn't care about the checksum though. > > > Maybe we need a flag > > to say which offloads are expensive? > > > > That exposes some device details which seem not good (e.g we may want > to do migration among hardware and software). > > Thanks If you do then things will be less well tuned on one of the migration ends but then that is by design, isn't it? -- MST 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. 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