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. > 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-unsubscr...@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscr...@lists.oasis-open.org For additional commands, e-mail: virtio-dev-h...@lists.oasis-open.org