> 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. iirc the blocking point was the missing CHECKSUM_COMPLETE support (we support just CHECKSUM_UNNECESSARY). We can conver it with XDP hw-hints. Regards, Lorenzo > > > > > 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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