[PATCH v7 net-next] virtio-net: support XDP when not more queues

Jason Wang
2021-03-09T02:17:16Z

On 2021/3/8 4:52 ??, Xuan Zhuo 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/XDP_REDIRECT, then xdp cannot be loaded to work, even xdp does
> not use the XDP_TX/XDP_REDIRECT.
>
> This patch allows XDP_TX/XDP_REDIRECT to run by reuse the existing SQ
> with __netif_tx_lock() hold when there are not enough queues.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> Reviewed-by: Dust Li <dust.li at linux.alibaba.com>
> ---
> v7: 1. use macros to implement get/put
>      2. remove 'flag'. (suggested by Jason Wang)
>
> v6: 1. use __netif_tx_acquire()/__netif_tx_release(). (suggested by Jason
Wang)
>      2. add note for why not lock. (suggested by Jason Wang)
>      3. Use variable 'flag' to record with or without locked.  It
is not safe to
>         use curr_queue_pairs in "virtnet_put_xdp_sq", because it
may changed after
>         "virtnet_get_xdp_sq".
>
> v5: change subject from 'support XDP_TX when not more queues'
>
> v4: make sparse happy
>      suggested by Jakub Kicinski
>
> v3: add warning when no more queues
>      suggested by Jesper Dangaard Brouer
>
>   drivers/net/virtio_net.c | 55
++++++++++++++++++++++++++++++++++++------------
>   1 file changed, 42 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ba8e637..5ce40ec 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;
>
> @@ -481,12 +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)
> -{
> -	unsigned int qp;
> -
> -	qp = vi->curr_queue_pairs - vi->xdp_queue_pairs +
smp_processor_id();
> -	return &vi->sq[qp];
> +/* when vi->curr_queue_pairs > nr_cpu_ids, the txq/sq is only used
for xdp tx on
> + * the current cpu, so it does not need to be locked.
> + */
> +#define virtnet_xdp_get_sq(vi) ({
\
> +	struct netdev_queue *txq;                                         \
> +	typeof(vi) v = (vi);                                              \


Any reason for not using vi directly?

Other looks good.

Thanks


> +	unsigned int qp;                                                  \
> +	if (v->curr_queue_pairs > nr_cpu_ids) {                           \
> +		qp = v->curr_queue_pairs - v->xdp_queue_pairs;            \
> +		qp += smp_processor_id();                                 \
> +		txq = netdev_get_tx_queue(v->dev, qp);                    \
> +		__netif_tx_acquire(txq);                                  \
> +	} else {                                                          \
> +		qp = smp_processor_id() % v->curr_queue_pairs;            \
> +		txq = netdev_get_tx_queue(v->dev, qp);                    \
> +		__netif_tx_lock(txq, raw_smp_processor_id());             \
> +	}                                                                 \
> +	v->sq + qp;                                                       \
> +})
> +
> +#define virtnet_xdp_put_sq(vi, q) {
\
> +	struct netdev_queue *txq;                                         \
> +	typeof(vi) v = (vi);                                              \
> +	txq = netdev_get_tx_queue(v->dev, (q) - v->sq);                   \
> +	if (v->curr_queue_pairs > nr_cpu_ids)                             \
> +		__netif_tx_release(txq);                                  \
> +	else                                                              \
> +		__netif_tx_unlock(txq);                                   \
>   }
>
>   static int virtnet_xdp_xmit(struct net_device *dev,
> @@ -512,7 +537,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>   	if (!xdp_prog)
>   		return -ENXIO;
>
> -	sq = virtnet_xdp_sq(vi);
> +	sq = virtnet_xdp_get_sq(vi);
>
>   	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) {
>   		ret = -EINVAL;
> @@ -560,12 +585,13 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>   	sq->stats.kicks += kicks;
>   	u64_stats_update_end(&sq->stats.syncp);
>
> +	virtnet_xdp_put_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 +1483,13 @@ 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_xdp_get_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_xdp_put_sq(vi, sq);
>   	}
>
>   	return received;
> @@ -2417,10 +2444,9 @@ static int virtnet_xdp_set(struct net_device *dev,
struct bpf_prog *prog,
>
>   	/* 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",
> +		netdev_warn(dev, "XDP request %i queues but max is %i. XDP_TX and
XDP_REDIRECT will operate in a slower locked tx mode.\n",
>   			    curr_qp + xdp_qp, vi->max_queue_pairs);
> -		return -ENOMEM;
> +		xdp_qp = 0;
>   	}
>
>   	old_prog = rtnl_dereference(vi->rq[0].xdp_prog);
> @@ -2454,11 +2480,14 @@ 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 +2555,7 @@ 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
>