Jason Wang
2021-Mar-05 07:08 UTC
[PATCH v5 net-next] virtio-net: support XDP when not more queues
On 2021/3/1 11:22 ??, 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> > --- > 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 >