Re: [PATCH vhost 17/17] virtio_net: sq support premapped mode

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Wed, 31 Jan 2024 17:12:47 +0800, Jason Wang <jasowang@redhat.com> wrote:
> On Tue, Jan 30, 2024 at 7:43 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> >
> > If the xsk is enabling, the xsk tx will share the send queue.
> > But the xsk requires that the send queue use the premapped mode.
> > So the send queue must support premapped mode.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > ---
> >  drivers/net/virtio_net.c | 167 ++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 163 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 226ab830870e..cf0c67380b07 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -46,6 +46,7 @@ module_param(napi_tx, bool, 0644);
> >  #define VIRTIO_XDP_REDIR       BIT(1)
> >
> >  #define VIRTIO_XDP_FLAG        BIT(0)
> > +#define VIRTIO_DMA_FLAG        BIT(1)
> >
> >  /* RX packet size EWMA. The average packet size is used to determine the packet
> >   * buffer size when refilling RX rings. As the entire RX ring may be refilled
> > @@ -140,6 +141,21 @@ struct virtnet_rq_dma {
> >         u16 need_sync;
> >  };
> >
> > +struct virtnet_sq_dma {
> > +       union {
> > +               struct virtnet_sq_dma *next;
> > +               void *data;
> > +       };
> > +       dma_addr_t addr;
> > +       u32 len;
> > +       bool is_tail;
> > +};
> > +
> > +struct virtnet_sq_dma_head {
> > +       struct virtnet_sq_dma *free;
> > +       struct virtnet_sq_dma *head;
> 
> Any reason the head must be a pointer instead of a simple index?


The head is used for kfree.
Maybe I need to rename it.

About the index(next) of the virtnet_sq_dma.
If we use the index, the struct will be:

struct virtnet_sq_dma {
       dma_addr_t addr;
       u32 len;

       u32 next;
       void *data
};

The size of virtnet_sq_dma is same. 


> 
> > +};
> > +
> >  /* Internal representation of a send virtqueue */
> >  struct send_queue {
> >         /* Virtqueue associated with this send _queue */
> > @@ -159,6 +175,8 @@ struct send_queue {
> >
> >         /* Record whether sq is in reset state. */
> >         bool reset;
> > +
> > +       struct virtnet_sq_dma_head dmainfo;
> >  };
> >

....

> > +
> > +static int virtnet_sq_init_dma_mate(struct send_queue *sq)
> > +{
> > +       struct virtnet_sq_dma *d;
> > +       int size, i;
> > +
> > +       size = virtqueue_get_vring_size(sq->vq);
> > +
> > +       size += MAX_SKB_FRAGS + 2;
> 
> Is this enough for the case where an indirect descriptor is used?


This is for the case, when the ring is full, the xmit_skb is called.

I will add comment.

Thanks.


> 
> Thanks
>