[PATCH v2 net-next] virtio-net: support XDP_TX when not more queues

* [PATCH v2 net-next] virtio-net: support XDP_TX when not more queues
@ 2021-02-25  8:22 Xuan Zhuo
  2021-02-25 17:01   ` Jesper Dangaard Brouer
  0 siblings, 1 reply; 4+ messages in thread
From: Xuan Zhuo @ 2021-02-25  8:22 UTC (permalink / raw)
  To: netdev
  Cc: Michael S. Tsirkin, Jason Wang, David S. Miller, Jakub Kicinski,
	Alexei Starovoitov, Daniel Borkmann, Jesper Dangaard Brouer,
	John Fastabend, virtualization, bpf

The number of queues implemented by many virtio backends is limited,
especially some machines have a large number of CPUs. In this case, it
is often impossible to allocate a separate queue for XDP_TX.

This patch allows XDP_TX to run by reuse the existing SQ with
__netif_tx_lock() hold when there are not enough queues.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
---
 drivers/net/virtio_net.c | 48 ++++++++++++++++++++++++++++++++++++------------
 1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ba8e637..c66ce4c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -195,6 +195,9 @@ struct virtnet_info {
 	/* # of XDP queue pairs currently used by the driver */
 	u16 xdp_queue_pairs;
 
+	/* xdp_queue_pairs may be 0, when xdp is already loaded. So add this. */
+	bool xdp_enabled;
+
 	/* I like... big packets and I cannot lie! */
 	bool big_packets;
 
@@ -481,14 +484,34 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
 	return 0;
 }
 
-static struct send_queue *virtnet_xdp_sq(struct virtnet_info *vi)
+static struct send_queue *virtnet_get_xdp_sq(struct virtnet_info *vi)
 {
+	struct netdev_queue *txq;
 	unsigned int qp;
 
-	qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
+	if (vi->curr_queue_pairs > nr_cpu_ids) {
+		qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
+	} else {
+		qp = smp_processor_id() % vi->curr_queue_pairs;
+		txq = netdev_get_tx_queue(vi->dev, qp);
+		__netif_tx_lock(txq, raw_smp_processor_id());
+	}
+
 	return &vi->sq[qp];
 }
 
+static void virtnet_put_xdp_sq(struct virtnet_info *vi, struct send_queue *sq)
+{
+	struct netdev_queue *txq;
+	unsigned int qp;
+
+	if (vi->curr_queue_pairs <= nr_cpu_ids) {
+		qp = sq - vi->sq;
+		txq = netdev_get_tx_queue(vi->dev, qp);
+		__netif_tx_unlock(txq);
+	}
+}
+
 static int virtnet_xdp_xmit(struct net_device *dev,
 			    int n, struct xdp_frame **frames, u32 flags)
 {
@@ -512,7 +535,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
 	if (!xdp_prog)
 		return -ENXIO;
 
-	sq = virtnet_xdp_sq(vi);
+	sq = virtnet_get_xdp_sq(vi);
 
 	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) {
 		ret = -EINVAL;
@@ -560,12 +583,13 @@ static int virtnet_xdp_xmit(struct net_device *dev,
 	sq->stats.kicks += kicks;
 	u64_stats_update_end(&sq->stats.syncp);
 
+	virtnet_put_xdp_sq(vi, sq);
 	return ret;
 }
 
 static unsigned int virtnet_get_headroom(struct virtnet_info *vi)
 {
-	return vi->xdp_queue_pairs ? VIRTIO_XDP_HEADROOM : 0;
+	return vi->xdp_enabled ? VIRTIO_XDP_HEADROOM : 0;
 }
 
 /* We copy the packet for XDP in the following cases:
@@ -1457,12 +1481,13 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 		xdp_do_flush();
 
 	if (xdp_xmit & VIRTIO_XDP_TX) {
-		sq = virtnet_xdp_sq(vi);
+		sq = virtnet_get_xdp_sq(vi);
 		if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
 			u64_stats_update_begin(&sq->stats.syncp);
 			sq->stats.kicks++;
 			u64_stats_update_end(&sq->stats.syncp);
 		}
+		virtnet_put_xdp_sq(vi, sq);
 	}
 
 	return received;
@@ -2416,12 +2441,8 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 		xdp_qp = nr_cpu_ids;
 
 	/* XDP requires extra queues for XDP_TX */
-	if (curr_qp + xdp_qp > vi->max_queue_pairs) {
-		NL_SET_ERR_MSG_MOD(extack, "Too few free TX rings available");
-		netdev_warn(dev, "request %i queues but max is %i\n",
-			    curr_qp + xdp_qp, vi->max_queue_pairs);
-		return -ENOMEM;
-	}
+	if (curr_qp + xdp_qp > vi->max_queue_pairs)
+		xdp_qp = 0;
 
 	old_prog = rtnl_dereference(vi->rq[0].xdp_prog);
 	if (!prog && !old_prog)
@@ -2454,11 +2475,14 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 	vi->xdp_queue_pairs = xdp_qp;
 
 	if (prog) {
+		vi->xdp_enabled = true;
 		for (i = 0; i < vi->max_queue_pairs; i++) {
 			rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
 			if (i == 0 && !old_prog)
 				virtnet_clear_guest_offloads(vi);
 		}
+	} else {
+		vi->xdp_enabled = false;
 	}
 
 	for (i = 0; i < vi->max_queue_pairs; i++) {
@@ -2526,7 +2550,7 @@ static int virtnet_set_features(struct net_device *dev,
 	int err;
 
 	if ((dev->features ^ features) & NETIF_F_LRO) {
-		if (vi->xdp_queue_pairs)
+		if (vi->xdp_enabled)
 			return -EBUSY;
 
 		if (features & NETIF_F_LRO)
-- 
1.8.3.1


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