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

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Message-ID: <willemdebruijn.kernel.359531d88f721@gmail.com>
Date: Thu, 22 Jan 2026 14:42:57 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Eric Dumazet <edumazet@...gle.com>, 
 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

Willem de Bruijn wrote:
> Eric Dumazet wrote:
> > 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.
> 
> What is the purpose of extending?
> 
> The current length is sufficient for standard Toeplitz 4-tuple hashing.

Never mind, I should read better:

> And the devices support hashing over two layers of IPv6 for tunnels.

I'm hard pressed to see over 128 B of entropy. But if extending, might
as well go to 256 B right away.