[virtio-dev] Re: [virtio-comment] [PATCH v15 10/11] virtio-net: Describe RSS using rss rq id

David Edmondson
2023-05-03T15:59:13Z

Parav Pandit <parav@nvidia.com> writes:

> The content of the indirection table and unclassified_queue were
> originally described based on mathematical operations. In order to
> make it easier to understand and to avoid intermixing the array
> index with the vq index, introduce a structure
> rss_rq_id (RSS receive queue
> ID) and use it to describe the unclassified_queue and
> indirection_table fields.
>
> As part of it, have the example that uses non-zero virtqueue
> index which helps to have better mapping between receiveX
> object with virtqueue index and the actual value in the
> indirection table.
>
> Fixes: https://github.com/oasis-tcs/virtio-spec/issues/163
> Signed-off-by: Parav Pandit <parav@nvidia.com>
>
> ---
> changelog:
> v14->v15:
> - address next comment from Michael and Halil
> - changed description of unclassified_queue to use 'specifies'
> v12->v13:
> - rename vqn to vq_index
> - renamed vq index to virtqueue index
> v11->v12:
> - use 'virtqueue index' instead of 'virtqueue number'
> v10->v11:
> - commit log updated to drop old reference to rq_handle, replaced with
> rss_rq_id detail
> v8->v9:
> - reword rss_rq_id and unclassified_packets description
> - use article
> - use 'vq number' instead of 'virtqueue number'
> v4->v5:
> - change subject to reflect rss_rq_id
> - fixed accidental removal of "unclassifed packets".
> - simplfied text around indirection_table mask to use the term
> destination receive virtqueue. This aligns with next line about queue
> reset.
> - removed rss_rq_id references as indirection table and
> unclassified_queue data type is self explanatory
> v3->v4:
> - renamed rq_handle to rss_rq_id
> - moved rss_rq_id definition close to its usage in rss_config struct
> v2->v3:
> - moved rq_handle definition before using it
> - removed duplicate example as rq_handle is now described first
> v0->v1:
> - new patch suggested by Michael Tsirkin
> ---
> device-types/net/description.tex | 27 ++++++++++++++++++++-------
> 1 file changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/device-types/net/description.tex b/device-types/net/description.tex
> index f3f9f1d..e25a9d0 100644
> --- a/device-types/net/description.tex
> +++ b/device-types/net/description.tex
> @@ -1434,11 +1434,16 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
>
> Driver sends a VIRTIO_NET_CTRL_MQ_RSS_CONFIG command using the following format for \field{command-specific-data}:
> \begin{lstlisting}
> +struct rss_rq_id {
> + le16 vq_index_1_16: 15; /* Bits 1 to 16 of the virtqueue index */
> + le16 reserved: 1; /* Set to zero */
> +};
> +
> struct virtio_net_rss_config {
> le32 hash_types;
> le16 indirection_table_mask;
> - le16 unclassified_queue;
> - le16 indirection_table[indirection_table_length];
> + 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];
> @@ -1453,10 +1458,15 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
> \field{indirection_table} array.
> Number of entries in \field{indirection_table} is (\field{indirection_table_mask} + 1).
>
> -Field \field{unclassified_queue} contains the 0-based index of
> -the receive virtqueue to place unclassified packets in. Index 0 corresponds to receiveq1.
> +\field{rss_rq_id} is a receive virtqueue id. \field{vq_index_1_16}
> +consists of bits 1 to 16 of a virtqueue index. For example, a
> +\field{vq_index_1_16} value of 3 corresponds to virtqueue index 6,
> +which maps to receiveq4.
> +
> +Field \field{unclassified_queue} specifies the receive virtqueue in which to
> +place unclassified packets.
>
> -Field \field{indirection_table} contains an array of 0-based indices of receive virtqueues. Index 0 corresponds to receiveq1.
> +Field \field{indirection_table} is an array of receive virtqueues.

...an array of receive virtqueue ids.

>
> A driver sets \field{max_tx_vq} to inform a device how many transmit virtqueues it may use (transmitq1\ldots transmitq \field{max_tx_vq}).
>
> @@ -1466,7 +1476,8 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
>
> A driver MUST NOT send the VIRTIO_NET_CTRL_MQ_RSS_CONFIG command if the feature VIRTIO_NET_F_RSS has not been negotiated.
>
> -A driver MUST fill the \field{indirection_table} array only with indices of enabled queues. Index 0 corresponds to receiveq1.
> +A driver MUST fill the \field{indirection_table} array only with
> +enabled receive virtqueues.
>
> The number of entries in \field{indirection_table} (\field{indirection_table_mask} + 1) MUST be a power of two.
>
> @@ -1479,7 +1490,9 @@ \subsubsection{Control Virtqueue}\label{sec:Device Types / Network Device / Devi
> \begin{itemize}
> \item Calculate the hash of the packet as defined in \ref{sec:Device Types / Network Device / Device Operation / Processing of Incoming Packets / Hash calculation for incoming packets}.
> \item If the device did not calculate the hash for the specific packet, the device directs the packet to the receiveq specified by \field{unclassified_queue} of virtio_net_rss_config structure.
> -\item Apply \field{indirection_table_mask} to the calculated hash and use the result as the index in the indirection table to get 0-based number of destination receiveq.
> +\item Apply \field{indirection_table_mask} to the calculated hash
> +and use the result as the index in the indirection table to get
> +the destination receive virtqueue.
> \item If the destination receive queue is being reset (See \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}), the device MUST drop the packet.
> \end{itemize}
>
> --
> 2.26.2
>
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