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Date: Tue, 14 Nov 2023 11:16:36 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
 <netdev@...r.kernel.org>,
 "David S.  Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Jakub  Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 Jason Wang <jasowang@...hat.com>,
 Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John  Fastabend <john.fastabend@...il.com>,
 <virtualization@...ts.linux-foundation.org>,
 <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next v2 16/21] virtio_net: xsk: rx: introduce add_recvbuf_xsk()

On Mon, 13 Nov 2023 17:00:50 +0100, Maciej Fijalkowski <maciej.fijalkowski@...el.com> wrote:
> On Fri, Nov 10, 2023 at 10:38:04AM +0800, Xuan Zhuo wrote:
> > On Thu, 9 Nov 2023 17:26:33 +0100, Maciej Fijalkowski <maciej.fijalkowski@...el.com> wrote:
> > > 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" <mst@...hat.com> 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 <xuanzhuo@...ux.alibaba.com>
> > > > > > ---
> > > > > >  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.
> >
> >
> > virtnet_add_recvbuf_xsk is called by the above try_fill_recv()
> > And the loop is in there.
>
> Ah sorry I was looking for another patch to call it as it used to be in
> v1.
>
> >
> > Jason want to reuse the loop of the try_fill_recv().
> > So in this function I just consume one item.
> >
> > The nxt_idx is used to cross the try_fill_recv.
> >
> > If we drop the nxt_idx. This patch will like this:
> >
> > diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
> > index 6210a6e37396..88bff83ad0d8 100644
> > --- a/drivers/net/virtio/main.c
> > +++ b/drivers/net/virtio/main.c
> > @@ -1797,6 +1797,15 @@ static bool try_fill_recv(struct virtnet_info *vi, struct virtnet_rq *rq,
> >  	int err;
> >  	bool oom;
> >
> > +	if (rq->xsk.pool) {
> > +		err = virtnet_add_recvbuf_xsk(vi, rq, rq->xsk.pool, gfp);
> > +		oom = err == -ENOMEM;
> > +		if (err > 0)
> > +			goto kick;
> > +
> > +		return err;
> > +	}
> > +
> >  	do {
> >  		if (vi->mergeable_rx_bufs)
> >  			err = add_recvbuf_mergeable(vi, rq, gfp);
> > @@ -1809,6 +1818,7 @@ static bool try_fill_recv(struct virtnet_info *vi, struct virtnet_rq *rq,
> >  		if (err)
> >  			break;
> >  	} while (rq->vq->num_free);
> > +kick:
> >  	if (virtqueue_kick_prepare(rq->vq) && virtqueue_notify(rq->vq)) {
> >  		unsigned long flags;
> >
> > diff --git a/drivers/net/virtio/virtio_net.h b/drivers/net/virtio/virtio_net.h
> > index a13d6d301fdb..184866014a19 100644
> > --- a/drivers/net/virtio/virtio_net.h
> > +++ b/drivers/net/virtio/virtio_net.h
> > @@ -140,6 +140,8 @@ struct virtnet_rq {
> >
> >  		/* xdp rxq used by xsk */
> >  		struct xdp_rxq_info xdp_rxq;
> > +
> > +		struct xdp_buff **xsk_buffs;
> >  	} xsk;
> >  };
> >
> > diff --git a/drivers/net/virtio/xsk.c b/drivers/net/virtio/xsk.c
> > index ea5804ddd44e..73c9323bffd3 100644
> > --- a/drivers/net/virtio/xsk.c
> > +++ b/drivers/net/virtio/xsk.c
> > @@ -38,6 +38,46 @@ 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;
> > +	int num;
> > +
> > +	xsk_buffs = rq->xsk.xsk_buffs;
> > +
> > +	num = xsk_buff_alloc_batch(pool, xsk_buffs, rq->vq->num_free);
> > +	if (!num)
> > +		return -ENOMEM;
> > +
> > +	for (i = 0; i < num; ++i) {
> > +		/* 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;
>
> len can be pulled out of loop...
>
> > +
> > +		sg_init_table(rq->sg, 1);
> > +		sg_fill_dma(rq->sg, addr, len);
>
> ... but when I first commented I did not understand why you were not
> passing dma from xsk_buff_pool like this:
>
> 	sg_init_table(rq->sg, num);
> 	len = xsk_pool_get_rx_frame_size(pool) + vi->hdr_len;
>
> 	for (i = 0; i < num; ++i) {
> 		/* use the part of XDP_PACKET_HEADROOM as the virtnet hdr space */
> 		addr = xsk_buff_xdp_get_dma(xsk_buffs[i]) - vi->hdr_len;
> 		/* TODO: extend scatterlist size in receive_queue */
> 		sg_fill_dma(&rq->sg[i], addr, len);
> 	}
>
> 	err = virtqueue_add_inbuf(rq->vq, rq->sg, num, xsk_buffs, gfp);


Yes, you are right.


>
> and now I see that the problem is with 'data' argument above (or xsk_buffs
> in this particular example).
>
> Why do you need to pass xdp_buff to virtio_ring? You already have the
> rq->xsk.xsk_buffs which you can use on rx side.
>
> Can someone shed some light on it?

For virtio, we should not assume that the virtio ring is consumed
sequentially by default.

So we normally use the "data" to distinguish the received buffers.

Thanks.


>
> > +
> > +		err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, xsk_buffs[i], gfp);
> > +		if (err)
> > +			goto err;
> > +	}
> > +
> > +	return num;
> > +
> > +err:
> > +	if (i)
> > +		err = i;
> > +
> > +	for (; i < num; ++i)
> > +		xsk_buff_free(xsk_buffs[i]);
> > +
> > +	return err;
> > +}
> > +
> >  static int virtnet_xsk_xmit_one(struct virtnet_sq *sq,
> >  				struct xsk_buff_pool *pool,
> >  				struct xdp_desc *desc)
> > @@ -213,7 +253,7 @@ 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 +289,12 @@ 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;
> > +
> >  	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 +353,8 @@ 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
> >
> >

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