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

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Message-ID: <1706757660.3554723-2-xuanzhuo@linux.alibaba.com>
Date: Thu, 1 Feb 2024 11:21:00 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: virtualization@...ts.linux.dev,
 Richard Weinberger <richard@....at>,
 Anton Ivanov <anton.ivanov@...bridgegreys.com>,
 Johannes Berg <johannes@...solutions.net>,
 "Michael S. Tsirkin" <mst@...hat.com>,
 "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 Hans de Goede <hdegoede@...hat.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Vadim Pasternak <vadimp@...dia.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Mathieu Poirier <mathieu.poirier@...aro.org>,
 Cornelia Huck <cohuck@...hat.com>,
 Halil Pasic <pasic@...ux.ibm.com>,
 Eric Farman <farman@...ux.ibm.com>,
 Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>,
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 Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>,
 Benjamin Berg <benjamin.berg@...el.com>,
 Yang Li <yang.lee@...ux.alibaba.com>,
 linux-um@...ts.infradead.org,
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Subject: Re: [PATCH vhost 17/17] virtio_net: sq support premapped mode

On Wed, 31 Jan 2024 17:12:47 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Tue, Jan 30, 2024 at 7:43 PM Xuan Zhuo <xuanzhuo@...ux.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@...ux.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
>