Re: [virtio-comment] [PATCH v2] virtio-net: Define per-packet hash reporting feature

[Yuri Benditovich <ybendito@redhat.com>]

----- Original Message ----- 

> From: "Michael S. Tsirkin" <mst@redhat.com>
> To: "Yuri Benditovich" <ybendito@redhat.com>
> Cc: "Yuri Benditovich" <yuri.benditovich@daynix.com>,
> virtio-comment@lists.oasis-open.org
> Sent: Monday, February 3, 2020 3:20:56 PM
> Subject: Re: [virtio-comment] [PATCH v2] virtio-net: Define per-packet hash
> reporting feature

> On Mon, Feb 03, 2020 at 08:10:57AM -0500, Yuri Benditovich wrote:
> > > > +\item The device uses \field{hash_key_data} of the
> > > > virtio_net_rss_config
> > > > structure.
> > > > +\end{itemize}
> > > > +See the definition of virtio_net_rss_config structure in
> > > > \ref{sec:Device
> > > > Types / Network Device / Device Operation / Control Virtqueue /
> > > > Receive-side scaling (RSS) / Setting RSS parameters}
> > > > +
> > > > +If the feature VIRTIO_NET_F_RSS was not negotiated, the device uses
> > > > internal configuration
> > > > +of enabled hash types and a key used for hash calculation.
> >
> > > I don't understand this last paragraph. Could you clarify?
> >
> > In order to calculate a hash the device shall have 2 things:
> > a key for hash calculation
> > a bitmask which hash types are enabled
> >
> > In case the device supportes RSS command (even with single queue), it can
> > take them from current RSS configuration.
> > If only VIRTIO_NET_F_HASH_REPORT is negotiated, the device uses internal
> > preset of both parameters.
> >
> > Do you suggest something different?

> Hmm control over key/mask would be nice to have.
> I guess we could add a command along the lines of:

> struct virtio_net_hash_config {
> le32 hash_types;
> le16 reserved[4];
> u8 hash_key_length;
> u8 hash_key_data[hash_key_length];
> };

> This needs some thought: we don't want to request that devices have
> double the machinery so the command should not be there if RSS is
> enabled ...

> Maybe the command is only valid if HASH is set but RSS is clear?

No problem.
To avoid further ping-pongs:
What is this reserved[4] needed for?
Please confirm:
- this is an additional command under VIRTIO_NET_CTRL_MQ
- should be supported when HASH_REPORT is negotiated, with or without MQ, not needed if RSS supported
- Initially all hashes are disabled

> --
> MST

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