Re: [virtio-dev] RE: [virtio-comment] RE: [PATCH v19] virtio-net: support inner header hash

[Heng Qi <hengqi@linux.alibaba.com>]

On Thu, Jun 29, 2023 at 04:59:28PM +0000, Parav Pandit wrote:
> 
> 
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Thursday, June 29, 2023 7:48 AM
> 
> 
> > > > struct virtio_net_hash_config reserved is fine.
> > >
> > > +1.
> > >
> > > Inner header hash is orthogonal to RSS, and it's fine to have its own
> > > structure and commands.
> > > There is no need to send additional RSS fields when we configure inner
> > > header hash.
> > >
> > > Thanks.
> > 
> > Not RSS, hash calculations. It's not critical, but I note that practically you said
> > you will enable this with symmetric hash so it makes sense to me to send this in
> > the same command with the key.
> > 
> 
> In the v19, we have,
> 
> +\item[VIRTIO_NET_F_HASH_TUNNEL] Requires VIRTIO_NET_F_CTRL_VQ along with VIRTIO_NET_F_RSS or VIRTIO_NET_F_HASH_REPORT.
> 
> So it is done along with rss, so in same struct as rss config is fine.

Do you mean having both virtio_net_rss_config and virtio_net_hash_config
have enabled_hash_types?
Like this:

struct virtio_net_rss_config {
     le32 hash_types;
     le16 indirection_table_mask;
     struct rss_rq_id unclassified_queue;
     struct rss_rq_id indirection_table[indirection_table_length];
     le16 max_tx_vq;
     u8 hash_key_length;
     u8 hash_key_data[hash_key_length];
+    le32 enabled_tunnel_types;	
};

struct virtio_net_hash_config {
     le32 hash_types;
-    le16 reserved[4];
+    le32 enabled_tunnel_types;
+    le16 reserved[2];
     u8 hash_key_length;
     u8 hash_key_data[hash_key_length];
};


If yes, this should have been discussed in v10 [1] before, enabled_tunnel_types in virtio_net_rss_config
will follow the variable length field and cause misalignment.

If we let the inner header hash reuse the virtio_net_hash_config structure, it can work, but the only disadvantage
is that the configuration of the inner header hash and *RSS*(not hash calculations) becomes somewhat coupled.
Just imagine:
If the driver and the device negotiated VIRTIO_NET_F_HASH_TUNNEL and VIRTIO_NET_F_RSS, but did not negotiate VIRTIO_NET_F_HASH_REPORT,
1. then if we only want to configure the inner header hash (such as enabled_tunnel_types), it is good for us to send
virtio_net_hash_config alone;
2. but then if we want to configure the inner header hash and RSS (such as indirection table), we need to send all
virtio_net_rss_config and virtio_net_hash_config once, because virtio_net_rss_config now does not carry enabled_tunnel_types
due to misalignment.

So, I think the following structure will make it clearer to configure inner header hash and RSS/hash calculation.
But in any case, if we still propose to reuse virtio_net_hash_config proposal, I am ok, no objection:

1. The supported_tunnel_types are placed in the device config space;

2.
Reserve the following structure:

      struct virtnet_hash_tunnel {
le32 enabled_tunnel_types;
      };

3. Reserve the SET command for enabled_tunnel_types and remove the GET
command for enabled_tunnel_types.

[1] https://lists.oasis-open.org/archives/virtio-dev/202303/msg00317.html

Thanks a lot!

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