On 2021/3/1 11:22 上午, 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@xxxxxxxxxxxxxxxxx>
Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
---
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 | 53 ++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 44 insertions(+), 9 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index ba8e637..55f1dd1 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 +484,42 @@ 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)
+ __acquires(lock)
{
+ 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();
+
+ /* tell sparse we took the lock, but don't really take it */
+ __acquire(lock);
The code can explain itself but you need to explain why we don't need to
hold tx lock here.
And it looks to me we should use __netif_tx_acquire()/__netif_tx_release()?
Btw, is it better to refactor the code then we can annote the code with
something like __acquire(txq->xmit_lock)?
Thanks
+ } 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)
+ __releases(lock)
+{
+ 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);
+ } else {
+ /* make sparse happy */
+ __release(lock);
+ }
+}
+
static int virtnet_xdp_xmit(struct net_device *dev,
int n, struct xdp_frame **frames, u32 flags)
{
@@ -512,7 +543,7 @@ 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 +591,13 @@ 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 +1489,13 @@ 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;
@@ -2417,10 +2450,9 @@ 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 +2486,14 @@ 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 +2561,7 @@ 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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