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

[Parav Pandit <parav@nvidia.com>]

> From: Heng Qi <hengqi@linux.alibaba.com>
> Sent: Thursday, June 29, 2023 8:54 PM
> 
> 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;
>
Yes. I forgot the variable length part.
 
The second disadvantage I remember now is one need to resupply all the rss hash config parameter and device needs to compare and modify for this one field.

Given these two disadvantages, I also prefer independent SET command the way you have it.
 
> 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!