diff mbox series

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

Message ID 1614241349-77324-1-git-send-email-xuanzhuo@linux.alibaba.com
State Superseded
Headers show
Series [v2,net-next] virtio-net: support XDP_TX when not more queues | expand

Commit Message

Xuan Zhuo Feb. 25, 2021, 8:22 a.m. UTC 
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(-)

Comments

Jesper Dangaard Brouer Feb. 25, 2021, 5:01 p.m. UTC | #1 
On Thu, 25 Feb 2021 16:22:29 +0800
Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:

> 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
[...]
> @@ -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;

I think we should keep a netdev_warn message, but as a warning (not
error) that this will cause XDP_TX and XDP_REDIRECT to be slower on
this device due to too few free TX rings available.

In the future, we can mark a XDP features flag that this device is
operating in a slower "locked" Tx mode.

>  
>  	old_prog = rtnl_dereference(vi->rq[0].xdp_prog);
>  	if (!prog && !old_prog)
diff mbox series

Patch

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)