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

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Message-ID: <20240915124835.456676f0@hermes.local>
Date: Sun, 15 Sep 2024 12:48:35 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Jonathan Corbet <corbet@....net>, Willem de Bruijn
 <willemdebruijn.kernel@...il.com>, Jason Wang <jasowang@...hat.com>, "David
 S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Michael S.
 Tsirkin" <mst@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Shuah
 Khan <shuah@...nel.org>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org, kvm@...r.kernel.org,
 virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org,
 Yuri Benditovich <yuri.benditovich@...nix.com>, Andrew Melnychenko
 <andrew@...nix.com>
Subject: Re: [PATCH RFC v3 0/9] tun: Introduce virtio-net hashing feature

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