Re: [virtio-dev] RE: [PATCH v15] virtio-net: support inner header hash

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jun 08, 2023 at 02:26:51PM +0000, Parav Pandit wrote:
> 
> > From: Heng Qi <hengqi@linux.alibaba.com>
> > Sent: Thursday, June 8, 2023 2:41 AM
> 
> [..]
> > > > +The device MUST calculate the inner header hash for the configured
> > > > \field{hash_tunnel_types} without the outer UDP header if
> > > > \field{hash_option} is 1.
> > > > +
> > > This I think conflicts with the current RSS where if this override (higher priority
> > than RSS) or not.
> > 
> > VIRTIO_NET_F_HASH_TUNNEL instructs the device to calculate an inner header
> > hash for configured tunnel types.
> > Then, which fields are used for the calculation of the inner header hash is
> > determined by the RSS configuration.
> > 
> > Therefore, if the inner header hash uses \field{hash_option} to indicate that the
> > outer source UDP port is used to calculate the hash, it overrides the RSS
> > configuration (higher priority than RSS). It now not only indicates for which
> > tunnel types the inner hash should be calculated, but also indicates which fields
> > participate in the RSS hash calculation.
> > 
> > At this point, we can
> > 1. continue to allow this behavior. That is, if \field{hash_option} is set to 1, the
> > hash value calculated based on the outer source port indicated by
> > VIRTIO_NET_F_HASH_TUNNEL is provided to the indirection table to select the
> > rxq instead of the hash value provided by RSS.
> > 
> > 2. hand over to RSS the ability to specify a hash based on the outer source port.
> > That is, we can add VIRTIO_NET_RSS_HASH_TUNNEL_SRC_PORT_UDP_{v4, v6,
> > EX} in \field{supported_hash_types} to indicate that the hash should be
> > calculated using the outer source port for all UDP tunneling protocols.
> > This approach removes the need for \field{hash_option} and makes the line
> > between VIRTIO_NET_F_HASH_TUNNEL and VIRTIO_NET_F_RSS clearer.
> > 
> #2 is preferred.
> 
> But I must be missing something.
> Without VIRTIO_NET_RSS_HASH_TUNNEL_SRC_PORT_UDP_X, today if one wants to do RSS based on the outer UDP ports,
> It is already supported by the RSS (even in presence of the inner header).
> 
> So why do have to introduce VIRTIO_NET_RSS_HASH_TUNNEL_SRC_PORT_UDP_X?

they want an option to ignore all other header fields.

-- 
MST