linux-kernel - Re: [PATCH net-next v7 3/6] tun: Introduce virtio-net hash feature

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Message-ID: <20250305175204.GP3666230@kernel.org>
Date: Wed, 5 Mar 2025 17:52:04 +0000
From: Simon Horman <horms@...nel.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>,
	Stephen Hemminger <stephen@...workplumber.org>,
	gur.stavi@...wei.com, Lei Yang <leiyang@...hat.com>
Subject: Re: [PATCH net-next v7 3/6] tun: Introduce virtio-net hash feature

On Fri, Feb 28, 2025 at 04:58:49PM +0900, Akihiko Odaki wrote:
> Hash reporting
> --------------
> 
> Allow the guest to reuse the hash value to make receive steering
> consistent between the host and guest, and to save hash computation.
> 
> RSS
> ---

Odaki-san,

Please reformat the patch description to avoid including "^---$".
Git will truncate the commit message at that point,
excluding the text below and your Signed-off-by line.

> 
> RSS is a receive steering algorithm that can be negotiated to use with
> virtio_net. 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 steering program.
> 
> Introduce the code to perform RSS 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 I didn't
> opt for it because extending the current mechanism of eBPF steering
> program as is because it relies on legacy context rewriting, and
> introducing kfunc-based eBPF will result in non-UAPI dependency while
> the other relevant virtualization APIs such as KVM and vhost_net are
> UAPIs.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---

This one is ok, as the commit message should end here.

>  Documentation/networking/tuntap.rst |   7 ++
>  drivers/net/Kconfig                 |   1 +
>  drivers/net/tap.c                   |  62 ++++++++++++-
>  drivers/net/tun.c                   |  89 ++++++++++++++----
>  drivers/net/tun_vnet.h              | 180 +++++++++++++++++++++++++++++++++---
>  include/linux/if_tap.h              |   2 +
>  include/linux/skbuff.h              |   3 +
>  include/uapi/linux/if_tun.h         |  75 +++++++++++++++
>  net/core/skbuff.c                   |   4 +
>  9 files changed, 390 insertions(+), 33 deletions(-)

...