Re: [virtio-dev] [PATCH v14] virtio-net: support the virtqueue coalescing moderation

[Parav Pandit <parav@nvidia.com>]

On 4/4/2023 1:44 PM, Michael S. Tsirkin wrote:
> On Tue, Apr 04, 2023 at 04:32:07PM +0000, Parav Pandit wrote:
> > > From: Halil Pasic <pasic@linux.ibm.com>
> > > Sent: Tuesday, April 4, 2023 12:29 PM
> > >
> > > On Thu, 23 Mar 2023 23:24:22 +0800
> > > Heng Qi <hengqi@linux.alibaba.com> wrote:
> > >
> > > > +struct virtio_net_ctrl_coal_vq {
> > > > +    le16 vqn;
> > > > +    le16 reserved;
> > > > +    struct virtio_net_ctrl_coal coal; };
> > > > +
> > > >   #define VIRTIO_NET_CTRL_NOTF_COAL 6
> > > >    #define VIRTIO_NET_CTRL_NOTF_COAL_TX_SET  0
> > > >    #define VIRTIO_NET_CTRL_NOTF_COAL_RX_SET 1
> > > > + #define VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET 2 #define
> > > > + VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET 3
> > > >   \end{lstlisting}
> > > >
> > > >   Coalescing parameters:
> > > >   \begin{itemize}
> > > > +\item \field{vqn}: The virtqueue number of an enabled transmit or receive
> > > virtqueue.
> > >
> > > Just to be on the safe side: VIRTIO_F_NOTIF_CONFIG_DATA has been
> > > negotiated, and queue_select != queue_notify_data, is vqn supposed to contain
> > > queue_notify_data or the number/index that is used for queue_select (I'm
> > > talking about the PCI transport case)?
> > Vqn has zero relation to notification config data feature and featue bit.
> > It is the real vqn enabled via queue_select.
> >
> > Once the vqn is renamed to vq_notify_id, we won't have this confusion anymore.
>
> vqn here is the index. queue_select is also the index.
Yes to both. No plan to rename them.

> Inside notifications-le.c we have:
> le32 {
>          vqn : 16;
>          next_off : 15;
>          next_wrap : 1;
> };
>
> vqn here is queue_notify_data.
vqn in above unnamed structure is contain
a. either vq index if CONFIG_DATA is not negotiated
or
b. it contains queue_notifiy_data if CONFIG_DATA is negotiated

Therefore, instead of naming it as vqn, renaming it to vq_notify_id 
crisply describe what it is for.

And not some vqn n stands for notification, but "d" of data is dropped 
somehow.

A notification identifier contains depending on negotiated feature bit.

>