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

[Parav Pandit <parav@nvidia.com>]

> From: Michael S. Tsirkin <mst@redhat.com>
> Sent: Tuesday, April 4, 2023 4:14 PM
> 
> On Tue, Apr 04, 2023 at 03:39:21PM -0400, Parav Pandit wrote:
> >
> >
> > 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.
> 
> vqnd then? for virt queue notification data?
> 
"id" identifies the queue as opposed to "data" identifying a queue.

> 
> > A notification identifier contains depending on negotiated feature bit.
> 
> it's not necessarily an identifier. can be e.g. just 0 for all vqs.
> whatever the device needs.
For driver its just an id, content doesn't matter.