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

Xuan Zhuo
2023-11-10T02:43:38Z

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.

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;
+
+ 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)
+ 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