Hello,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.
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. 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.
The XDP multi-buffer support needed for TSO/GSO seems to be mostly there already, but, to our understanding, the last missing part for full TSO/GSO support is a way to tell the physical NIC to perform the TSO/GSO offload.
I've seen the latest LPC 2022 talk from Jesper Dangaard Brouer regarding the planned XDP-Hints feature. But this was mainly about Checksum and VLAN offloads. Is supporting TSO/GSO also one of the goals you have in mind with these XDP-Hints proposals?
Will the multi-buffer and hints patches be all what's needed to make XDP_REDIRECT between a VM (without disabled offloads) and the host NIC possible, or are there more things missing in XDP that will become an issue in that use-case?
The "XDP Cloud-Provider" project page describes a very similar use-case to what we plan to do. What's the goal of this project?
We're very interested in the work on XDP-Hints and in the performance benefits that the offloading support could bring to XDP and I would be thankful if you could help us with some of our questions.
Best regards, Marcus Wichelmann Hetzner Cloud GmbH
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