Re: [PATCH RFC v3 0/9] tun: Introduce virtio-net hashing feature

[Stephen Hemminger]

On Sun, 15 Sep 2024 10:17:39 +0900
Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:

> virtio-net have two usage of hashes: one is RSS and another is hash
> reporting. Conventionally the hash calculation was done by the VMM.
> However, computing the hash after the queue was chosen defeats the
> purpose of RSS.
> 
> Another approach is to use eBPF steering program. This approach has
> another downside: it cannot report the calculated hash due to the
> restrictive nature of eBPF.
> 
> Introduce the code to compute hashes to the kernel in order to overcome
> thse challenges.
> 
> An alternative solution is to extend the eBPF steering program so that it
> will be able to report to the userspace, but it is based on context
> rewrites, which is in feature freeze. We can adopt kfuncs, but they will
> not be UAPIs. We opt to ioctl to align with other relevant UAPIs (KVM
> and vhost_net).

This will be useful for DPDK. But there still are cases where custom
flow rules are needed. I.e the RSS happens after other TC rules.
It would be a good if skbedit supported RSS as an option.