Re: [PATCH net-next v11 00/10] tun: Introduce virtio-net hashing feature

[Jason Wang]

On Mon, Mar 17, 2025 at 6:58 PM 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).
>
> The patches for QEMU to use this new feature was submitted as RFC and
> is available at:
> https://patchew.org/QEMU/20250313-hash-v4-0-c75c494b495e@xxxxxxxxxx/
>
> This work was presented at LPC 2024:
> https://lpc.events/event/18/contributions/1963/
>
> V1 -> V2:
>   Changed to introduce a new BPF program type.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
> ---
> Changes in v11:
> - Added the missing code to free vnet_hash in patch
>   "tap: Introduce virtio-net hash feature".
> - Link to v10: https://lore.kernel.org/r/20250313-rss-v10-0-3185d73a9af0@xxxxxxxxxx
>

We only have 2 or 3 points that need to be sorted out. Let's hold on
to the iteration until we had an agreement.

Thanks