netdev - Re: [PATCH net-next] virtio_net: Increase RSS max key size to match NETDEV_RSS_KEY

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Message-ID: <CANn89iL5s+egLhothNtnQf0jtAeftezUjNmbuXtUWgfVV3+bzg@mail.gmail.com>
Date: Thu, 22 Jan 2026 17:13:55 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Srujana Challa <schalla@...vell.com>, Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org, 
	virtualization@...ts.linux.dev, pabeni@...hat.com, mst@...hat.com, 
	jasowang@...hat.com, xuanzhuo@...ux.alibaba.com, eperezma@...hat.com, 
	andrew+netdev@...n.ch, davem@...emloft.net, ndabilpuram@...vell.com, 
	Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net-next] virtio_net: Increase RSS max key size to match NETDEV_RSS_KEY_LEN

On Thu, Jan 22, 2026 at 4:52 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 22 Jan 2026 14:45:27 +0530 Srujana Challa wrote:
> > Increase VIRTIO_NET_RSS_MAX_KEY_SIZE from 40 to 52 bytes to align with
> > the kernel's standard RSS key length defined by NETDEV_RSS_KEY_LEN.
>
> I've been meaning to bump NETDEV_RSS_KEY_LEN to 128 or some such.
> Most modern drivers can't use netdev_rss_key_fill() either because
> core generates a tiny key. And the devices support hashing over two
> layers of IPv6 for tunnels.

Seems fine to me. Back in 2014, RSS was limited to 52 bytes on all known NIC.

>
> Willem, WDYT? Is there a reason to keep the core key small?
> Or deprecate netdev_rss_key_fill()?

What do you mean by deprecating it ?

One of the ideas was to make sure multiple NIC would share the same key,
for some bonding setups.

commit 960fb622f85180f36d3aff82af53e2be3db2f888    net: provide a per
host RSS key generic infrastructure



>
> > The virtio specification requires devices to support at least 40 bytes
> > for the RSS key size. However, devices may support larger key sizes
> > up to 52 bytes (as reported by the device's rss_max_key_size config
> > field). This change allows such devices to work properly.
> > Previously, devices reporting rss_max_key_size > 40 would fail with
> > an error during initialization.
> >
> > The driver already handles variable key sizes dynamically through
> > vi->rss_key_size, so increasing the maximum limit is safe and
> > maintains backward compatibility with devices that support smaller
> > key sizes.
>
> > -#define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
> > +#define VIRTIO_NET_RSS_MAX_KEY_SIZE     52