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

["Michael S. Tsirkin" <mst@redhat.com>]

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?


> 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.

> >