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Subject: Re: [virtio-dev] Re: [Proposal] Relationship between XDP and rx-csum in virtio-net
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: \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
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