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

Maciej Fijalkowski
2023-11-13T16:01:16Z

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@intel.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@redhat.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@linux.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);

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?

> +
> + 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
>
>