On 9/28/22 11:07 AM, Jesper Dangaard Brouer wrote: > > On 28/09/2022 15.54, Marcus Wichelmann wrote: >> >> I'm working for a cloud hosting provider and we're working on a new >> XDP-based networking stack for our VM-Hosts that uses XDP to >> accelerate the connectivity of our qemu/KVM VMs to the outside. >> > > Welcome to the community! Sounds like an excellent use-case and > opportunity for speeding up the RX packets from physical NIC into the > VM. Good to hear someone (again) having this use-case. I've personally +1 > not been focused on this use-case lately, mostly because community > members that I was interacting with changed jobs, away from cloud > hosting companies. Good to have a user back in this area! > > >> For this, we use XDP_REDIRECT to forward packets between the physical >> host NIC and the VM tap devices. The main issue we have now is, that >> our VM guests have some virtio NIC offloads enabled: rx/tx >> checksumming, TSO/GSO, GRO and Scatter-Gather. > > Supporting RX-checksumming is part of the plans for XDP-hints, although > virtio_net is not part of my initial patchset. Lorenzo and I both had versions of a patch to propagate rx csum validation to the VM on xdp redirect. I do not recall a version after this one: https://lore.kernel.org/netdev/cover.1622222367.git.lorenzo@xxxxxxxxxx/ and I lost of track of what change is needed for it to go in. > > XDP-redirect with GRO and Scatter-Gather frames are part of the > multi-buff effort (Cc Lorenzo), but currently XDP_REDIRECT with > multi-buff is disabled (except for cpumap), because the lack of > XDP-feature bits, meaning we cannot determine (in kernel) if receiving > net_device supports multi-buff (Cc Kumar). > >> Currently, these offloads (especially TSO/GSO) are incompatible with >> XDP_REDIRECT and result in packets being dropped. Because disabling >> these offloads in all our customer VMs is not a good option, we're >> searching for ways to support these offloads with XDP. >> > > To David Ahern, didn't the kernel recently loosen up on having to > disable these offloads for KVM virtio_net? not that I am aware. Still need tx offloads disabled. This summarizes what I was looking into back in 2020, along with the current state of XDP for VM use case: https://legacy.netdevconf.info/0x14/pub/slides/24/netdev-0x14-XDP-and-the-cloud.pdf source code is still on github too.
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