[PATCH 5.4 37/61] virtio-net: support XDP when not more queues

Sasha Levin
2021-08-24T17:17:07Z

From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

[ Upstream commit 97c2c69e1926260c78c7f1c0b2c987934f1dc7a1 ]

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@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/virtio_net.c | 62 +++++++++++++++++++++++++++++++---------
1 file changed, 49 insertions(+), 13 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 15453d6fcc23..36f8aeb113a8 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;

@@ -485,12 +488,41 @@ 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.
+ *
+ * Here we use marco instead of inline functions because we have to deal with
+ * three issues at the same time: 1. the choice of sq. 2. judge and execute the
+ * lock/unlock of txq 3. make sparse happy. It is difficult for two inline
+ * functions to perfectly solve these three problems at the same time.
+ */
+#define virtnet_xdp_get_sq(vi) ({ \
+ struct netdev_queue *txq; \
+ typeof(vi) v = (vi); \
+ 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,
@@ -516,7 +548,7 @@ 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;
@@ -564,12 +596,13 @@ out:
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:
@@ -1458,12 +1491,13 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
xdp_do_flush_map();

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;
@@ -2480,10 +2514,9 @@ 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);
@@ -2520,11 +2553,14 @@ 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++) {
@@ -2609,7 +2645,7 @@ 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)
--
2.30.2