Jason Wang
2021-Mar-08 07:16 UTC
[PATCH v6 net-next] virtio-net: support XDP when not more queues
On 2021/3/8 1:43 ??, Xuan Zhuo wrote:> On Mon, 8 Mar 2021 11:41:03 +0800, Jason Wang <jasowang at redhat.com> wrote: >> On 2021/3/5 6:29 ??, 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> >>> --- >>> 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 | 63 ++++++++++++++++++++++++++++++++++++++++-------- >>> 1 file changed, 53 insertions(+), 10 deletions(-) >>> >>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>> index ba8e637..f9e024d 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 +484,48 @@ 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, int *flag) >>> + __acquires(txq->_xmit_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(); >>> + txq = netdev_get_tx_queue(vi->dev, qp); >>> + >>> + /* In this case, this txq is only used for xdp tx on the current >>> + * cpu, so it does not need to be locked. >>> + * __netif_tx_acquire is for sparse. >>> + */ >>> + __netif_tx_acquire(txq); >>> + *flag = false; >>> + } 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()); >>> + *flag = true; >>> + } >>> + >>> return &vi->sq[qp]; >> >> Two questions: >> >> 1) Can we simply check xdp_queue_paris against 0 then we don't need flag? >> 2) Can we pass txq to virtnet_get_xdp_sq() then the annotation looks >> even more better? >> >> Thanks > In this patch, I added xdp_enabled to determine the status of xdp, because > xdp_queue_pairs may be 0 when no more queues. > > But we can't use these to determine whether to unlock. Because after lock, this > variable may change, so we may make an error when we use this variable to > determine whether to unlock. > > When virtnet_get_xdp_sq is called by virtnet_xdp_xmit, it is actually safe to be > protected by rcu, but it is still called by virtnet_poll. This time is not safe. > It is possible that xdp_enabled will change after virtnet_get_xdp_sq.I think NAPI is disabled when we want to set/unset XDP. So xdp_qp can't be changed in virtnet_poll()? Thanks> So I think > it is a better choice to add a local variable to record whether to unlock. > > Regarding the second question, I think it's okay. In this way, the code for > get/put is very simple, I think it is better to use macros directly. > > ``` > static struct send_queue *virtnet_xdp_sq(struct virtnet_info *vi, int *flag) > { > unsigned int qp; > > if (vi->curr_queue_pairs > nr_cpu_ids) { > qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id(); > *flag = false; > } else { > qp = smp_processor_id() % vi->curr_queue_pairs; > *flag = true; > } > > return &vi->sq[qp]; > } > > #define virtnet_xdp_get_txq(vi, sq, flag) \ > if (flag) \ > __netif_tx_acquire(netdev_get_tx_queue(vi->dev, vq2txq(sq->vq))); \ > else \ > __netif_tx_lock(netdev_get_tx_queue(vi->dev, vq2txq(sq->vq)), \ > raw_smp_processor_id()); > > #define virtnet_xdp_put_txq(vi, sq, flag) \ > if (flag) \ > __netif_tx_unlock(netdev_get_tx_queue(vi->dev, vq2txq(sq->vq))); \ > else \ > __netif_tx_release(netdev_get_tx_queue(vi->dev, vq2txq(sq->vq))); > > > > sq = virtnet_xdp_sq(vi, &sq_flag); > virtnet_xdp_get_txq(vi, sq, sq_flag); > ....... > virtnet_xdp_put_txq(vi, sq, sq_flag); > ``` > > Do you think this is ok? @Jason > > thanks. > >> >>> } >>> >>> +static void virtnet_put_xdp_sq(struct virtnet_info *vi, struct send_queue *sq, >>> + int flag) >>> + __releases(txq->_xmit_lock) >>> +{ >>> + struct netdev_queue *txq; >>> + unsigned int qp; >>> + >>> + qp = sq - vi->sq; >>> + txq = netdev_get_tx_queue(vi->dev, qp); >>> + >>> + if (flag) >>> + __netif_tx_unlock(txq); >>> + else >>> + __netif_tx_release(txq); >>> +} >>> + >>> static int virtnet_xdp_xmit(struct net_device *dev, >>> int n, struct xdp_frame **frames, u32 flags) >>> { >>> @@ -496,12 +533,12 @@ static int virtnet_xdp_xmit(struct net_device *dev, >>> struct receive_queue *rq = vi->rq; >>> struct bpf_prog *xdp_prog; >>> struct send_queue *sq; >>> + int ret, err, sq_flag; >>> unsigned int len; >>> int packets = 0; >>> int bytes = 0; >>> int drops = 0; >>> int kicks = 0; >>> - int ret, err; >>> void *ptr; >>> int i; >>> >>> @@ -512,7 +549,7 @@ 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, &sq_flag); >>> >>> if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) { >>> ret = -EINVAL; >>> @@ -560,12 +597,13 @@ 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, sq_flag); >>> 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 +1495,15 @@ static int virtnet_poll(struct napi_struct *napi, int budget) >>> xdp_do_flush(); >>> >>> if (xdp_xmit & VIRTIO_XDP_TX) { >>> - sq = virtnet_xdp_sq(vi); >>> + int sq_flag; >>> + >>> + sq = virtnet_get_xdp_sq(vi, &sq_flag); >>> 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, sq_flag); >>> } >>> >>> return received; >>> @@ -2417,10 +2458,9 @@ 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 +2494,14 @@ 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 +2569,7 @@ 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 >>>