Subject: Re: [PATCH net-next v2 16/21] virtio_net: xsk: rx: introduce add_recvbuf_xsk()

From: Maciej Fijalkowski <[email-masked]>
Date: Thu, 9 Nov 2023 17:26:33 +0100

On Thu, Nov 09, 2023 at 07:11:46PM +0800, Xuan Zhuo wrote:
> On Thu, 9 Nov 2023 03:12:27 -0500, "Michael S. Tsirkin" <[email-masked]> wrote:
> > On Tue, Nov 07, 2023 at 11:12:22AM +0800, Xuan Zhuo wrote:
> > > Implement the logic of filling rq with XSK buffers.
> > >
> > > Signed-off-by: Xuan Zhuo <[email-masked]>
> > > ---
> > >  drivers/net/virtio/main.c       |  4 ++-
> > >  drivers/net/virtio/virtio_net.h |  5 ++++
> > >  drivers/net/virtio/xsk.c        | 49 ++++++++++++++++++++++++++++++++-
> > >  drivers/net/virtio/xsk.h        |  2 ++
> > >  4 files changed, 58 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
> > > index 6210a6e37396..15943a22e17d 100644
> > > --- a/drivers/net/virtio/main.c
> > > +++ b/drivers/net/virtio/main.c
> > > @@ -1798,7 +1798,9 @@ static bool try_fill_recv(struct virtnet_info *vi, struct virtnet_rq *rq,
> > >  	bool oom;
> > >
> > >  	do {
> > > -		if (vi->mergeable_rx_bufs)
> > > +		if (rq->xsk.pool)
> > > +			err = virtnet_add_recvbuf_xsk(vi, rq, rq->xsk.pool, gfp);
> > > +		else if (vi->mergeable_rx_bufs)
> > >  			err = add_recvbuf_mergeable(vi, rq, gfp);
> > >  		else if (vi->big_packets)
> > >  			err = add_recvbuf_big(vi, rq, gfp);
> >
> > I'm not sure I understand. How does this handle mergeable flag still being set?
> 
> 
> You has the same question as Jason.
> 
> So I think maybe I should put the handle into the
> add_recvbuf_mergeable and add_recvbuf_small.
> 
> Let me think about this.
> 
> 
> >
> >
> > > diff --git a/drivers/net/virtio/virtio_net.h b/drivers/net/virtio/virtio_net.h
> > > index a13d6d301fdb..1242785e311e 100644
> > > --- a/drivers/net/virtio/virtio_net.h
> > > +++ b/drivers/net/virtio/virtio_net.h
> > > @@ -140,6 +140,11 @@ struct virtnet_rq {
> > >
> > >  		/* xdp rxq used by xsk */
> > >  		struct xdp_rxq_info xdp_rxq;
> > > +
> > > +		struct xdp_buff **xsk_buffs;
> > > +		u32 nxt_idx;
> > > +		u32 num;
> > > +		u32 size;
> > >  	} xsk;
> > >  };
> > >
> > > diff --git a/drivers/net/virtio/xsk.c b/drivers/net/virtio/xsk.c
> > > index ea5804ddd44e..e737c3353212 100644
> > > --- a/drivers/net/virtio/xsk.c
> > > +++ b/drivers/net/virtio/xsk.c
> > > @@ -38,6 +38,41 @@ static void virtnet_xsk_check_queue(struct virtnet_sq *sq)
> > >  		netif_stop_subqueue(dev, qnum);
> > >  }
> > >
> > > +int virtnet_add_recvbuf_xsk(struct virtnet_info *vi, struct virtnet_rq *rq,
> > > +			    struct xsk_buff_pool *pool, gfp_t gfp)
> > > +{
> > > +	struct xdp_buff **xsk_buffs;
> > > +	dma_addr_t addr;
> > > +	u32 len, i;
> > > +	int err = 0;
> > > +
> > > +	xsk_buffs = rq->xsk.xsk_buffs;
> > > +
> > > +	if (rq->xsk.nxt_idx >= rq->xsk.num) {
> > > +		rq->xsk.num = xsk_buff_alloc_batch(pool, xsk_buffs, rq->xsk.size);
> > > +		if (!rq->xsk.num)
> > > +			return -ENOMEM;
> > > +		rq->xsk.nxt_idx = 0;
> > > +	}
> >
> > Another manually rolled linked list implementation.
> > Please, don't.
> 
> 
> The array is for speedup.
> 
> xsk_buff_alloc_batch will return many xsk_buff that will be more efficient than
> the xsk_buff_alloc.

But your sg list just contains a single entry?
I think that you have to walk through the xsk_buffs array, retrieve dma
addrs from there and have sg list sized to the value
xsk_buff_alloc_batch() returned.

I don't think your logic based on nxt_idx is needed. Please take a look
how other drivers use xsk_buff_alloc_batch().

I don't see callsites of virtnet_add_recvbuf_xsk() though.

> 
> Thanks.
> 
> >
> >
> > > +
> > > +	i = rq->xsk.nxt_idx;
> > > +
> > > +	/* use the part of XDP_PACKET_HEADROOM as the virtnet hdr space */
> > > +	addr = xsk_buff_xdp_get_dma(xsk_buffs[i]) - vi->hdr_len;
> > > +	len = xsk_pool_get_rx_frame_size(pool) + vi->hdr_len;
> > > +
> > > +	sg_init_table(rq->sg, 1);
> > > +	sg_fill_dma(rq->sg, addr, len);
> > > +
> > > +	err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, xsk_buffs[i], gfp);
> > > +	if (err)
> > > +		return err;
> > > +
> > > +	rq->xsk.nxt_idx++;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >  static int virtnet_xsk_xmit_one(struct virtnet_sq *sq,
> > >  				struct xsk_buff_pool *pool,
> > >  				struct xdp_desc *desc)
> > > @@ -213,7 +248,7 @@ static int virtnet_xsk_pool_enable(struct net_device *dev,
> > >  	struct virtnet_sq *sq;
> > >  	struct device *dma_dev;
> > >  	dma_addr_t hdr_dma;
> > > -	int err;
> > > +	int err, size;
> > >
> > >  	/* In big_packets mode, xdp cannot work, so there is no need to
> > >  	 * initialize xsk of rq.
> > > @@ -249,6 +284,16 @@ static int virtnet_xsk_pool_enable(struct net_device *dev,
> > >  	if (!dma_dev)
> > >  		return -EPERM;
> > >
> > > +	size = virtqueue_get_vring_size(rq->vq);
> > > +
> > > +	rq->xsk.xsk_buffs = kcalloc(size, sizeof(*rq->xsk.xsk_buffs), GFP_KERNEL);
> > > +	if (!rq->xsk.xsk_buffs)
> > > +		return -ENOMEM;
> > > +
> > > +	rq->xsk.size = size;
> > > +	rq->xsk.nxt_idx = 0;
> > > +	rq->xsk.num = 0;
> > > +
> > >  	hdr_dma = dma_map_single(dma_dev, &xsk_hdr, vi->hdr_len, DMA_TO_DEVICE);
> > >  	if (dma_mapping_error(dma_dev, hdr_dma))
> > >  		return -ENOMEM;
> > > @@ -307,6 +352,8 @@ static int virtnet_xsk_pool_disable(struct net_device *dev, u16 qid)
> > >
> > >  	dma_unmap_single(dma_dev, sq->xsk.hdr_dma_address, vi->hdr_len, DMA_TO_DEVICE);
> > >
> > > +	kfree(rq->xsk.xsk_buffs);
> > > +
> > >  	return err1 | err2;
> > >  }
> > >
> > > diff --git a/drivers/net/virtio/xsk.h b/drivers/net/virtio/xsk.h
> > > index 7ebc9bda7aee..bef41a3f954e 100644
> > > --- a/drivers/net/virtio/xsk.h
> > > +++ b/drivers/net/virtio/xsk.h
> > > @@ -23,4 +23,6 @@ int virtnet_xsk_pool_setup(struct net_device *dev, struct netdev_bpf *xdp);
> > >  bool virtnet_xsk_xmit(struct virtnet_sq *sq, struct xsk_buff_pool *pool,
> > >  		      int budget);
> > >  int virtnet_xsk_wakeup(struct net_device *dev, u32 qid, u32 flag);
> > > +int virtnet_add_recvbuf_xsk(struct virtnet_info *vi, struct virtnet_rq *rq,
> > > +			    struct xsk_buff_pool *pool, gfp_t gfp);
> > >  #endif
> > > --
> > > 2.32.0.3.g01195cf9f
> >
> >
>