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netdevsim: implement peer queue flow control

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Add flow control mechanism between paired netdevsim devices to stop the
TX queue during high traffic scenarios. When a receive queue becomes
congested (approaching NSIM_RING_SIZE limit), the corresponding transmit
queue on the peer device is stopped using netif_subqueue_try_stop().

Once the receive queue has sufficient capacity again, the peer's
transmit queue is resumed with netif_tx_wake_queue().

Key changes:
  * Add nsim_stop_peer_tx_queue() to pause peer TX when RX queue is full
  * Add nsim_start_peer_tx_queue() to resume peer TX when RX queue drains
  * Implement queue mapping validation to ensure TX/RX queue count match
  * Wake all queues during device unlinking to prevent stuck queues
  * Use RCU protection when accessing peer device references
  * wake the queues when changing the queue numbers
  * Remove IFF_NO_QUEUE given it will enqueue packets now

The flow control only activates when devices have matching TX/RX queue
counts to ensure proper queue mapping.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20250711-netdev_flow_control-v3-1-aa1d5a155762@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Breno Leitao
2025-07-11 10:06:59 -07:00
committed by Jakub Kicinski
parent 5777d1871b
commit ff2ac4df58
3 changed files with 85 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
drivers/net/netdevsim/bus.c
View File

@@ -384,6 +384,9 @@ static ssize_t unlink_device_store(const struct bus_type *bus, const char *buf,
err = 0;
RCU_INIT_POINTER(nsim->peer, NULL);
RCU_INIT_POINTER(peer->peer, NULL);
synchronize_net();
netif_tx_wake_all_queues(dev);
netif_tx_wake_all_queues(peer->netdev);
out_put_netns:
put_net(ns);

21
drivers/net/netdevsim/ethtool.c
View File

@@ -101,6 +101,22 @@ nsim_get_channels(struct net_device *dev, struct ethtool_channels *ch)
ch->combined_count = ns->ethtool.channels;
}
static void
nsim_wake_queues(struct net_device *dev)
{
struct netdevsim *ns = netdev_priv(dev);
struct netdevsim *peer;
synchronize_net();
netif_tx_wake_all_queues(dev);
rcu_read_lock();
peer = rcu_dereference(ns->peer);
if (peer)
netif_tx_wake_all_queues(peer->netdev);
rcu_read_unlock();
}
static int
nsim_set_channels(struct net_device *dev, struct ethtool_channels *ch)
{
@@ -113,6 +129,11 @@ nsim_set_channels(struct net_device *dev, struct ethtool_channels *ch)
return err;
ns->ethtool.channels = ch->combined_count;
/* Only wake up queues if devices are linked */
if (rcu_access_pointer(ns->peer))
nsim_wake_queues(dev);
return 0;
}

68
drivers/net/netdevsim/netdev.c
View File

@@ -37,7 +37,53 @@ MODULE_IMPORT_NS("NETDEV_INTERNAL");
#define NSIM_RING_SIZE 256
static int nsim_napi_rx(struct nsim_rq *rq, struct sk_buff *skb)
static void nsim_start_peer_tx_queue(struct net_device *dev, struct nsim_rq *rq)
{
struct netdevsim *ns = netdev_priv(dev);
struct net_device *peer_dev;
struct netdevsim *peer_ns;
struct netdev_queue *txq;
u16 idx;
idx = rq->napi.index;
rcu_read_lock();
peer_ns = rcu_dereference(ns->peer);
if (!peer_ns)
goto out;
/* TX device */
peer_dev = peer_ns->netdev;
if (dev->real_num_tx_queues != peer_dev->num_rx_queues)
goto out;
txq = netdev_get_tx_queue(peer_dev, idx);
if (!netif_tx_queue_stopped(txq))
goto out;
netif_tx_wake_queue(txq);
out:
rcu_read_unlock();
}
static void nsim_stop_tx_queue(struct net_device *tx_dev,
struct net_device *rx_dev,
struct nsim_rq *rq,
u16 idx)
{
/* If different queues size, do not stop, since it is not
* easy to find which TX queue is mapped here
*/
if (rx_dev->real_num_tx_queues != tx_dev->num_rx_queues)
return;
/* rq is the queue on the receive side */
netif_subqueue_try_stop(tx_dev, idx,
NSIM_RING_SIZE - skb_queue_len(&rq->skb_queue),
NSIM_RING_SIZE / 2);
}
static int nsim_napi_rx(struct net_device *tx_dev, struct net_device *rx_dev,
struct nsim_rq *rq, struct sk_buff *skb)
{
if (skb_queue_len(&rq->skb_queue) > NSIM_RING_SIZE) {
dev_kfree_skb_any(skb);
@@ -45,13 +91,22 @@ static int nsim_napi_rx(struct nsim_rq *rq, struct sk_buff *skb)
}
skb_queue_tail(&rq->skb_queue, skb);
/* Stop the peer TX queue avoiding dropping packets later */
if (skb_queue_len(&rq->skb_queue) >= NSIM_RING_SIZE)
nsim_stop_tx_queue(tx_dev, rx_dev, rq,
skb_get_queue_mapping(skb));
return NET_RX_SUCCESS;
}
static int nsim_forward_skb(struct net_device *dev, struct sk_buff *skb,
static int nsim_forward_skb(struct net_device *tx_dev,
struct net_device *rx_dev,
struct sk_buff *skb,
struct nsim_rq *rq)
{
return __dev_forward_skb(dev, skb) ?: nsim_napi_rx(rq, skb);
return __dev_forward_skb(rx_dev, skb) ?:
nsim_napi_rx(tx_dev, rx_dev, rq, skb);
}
static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
@@ -86,7 +141,7 @@ static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
skb_linearize(skb);
skb_tx_timestamp(skb);
if (unlikely(nsim_forward_skb(peer_dev, skb, rq) == NET_RX_DROP))
if (unlikely(nsim_forward_skb(dev, peer_dev, skb, rq) == NET_RX_DROP))
goto out_drop_cnt;
if (!hrtimer_active(&rq->napi_timer))
@@ -351,6 +406,7 @@ static int nsim_rcv(struct nsim_rq *rq, int budget)
dev_dstats_rx_dropped(dev);
}
nsim_start_peer_tx_queue(dev, rq);
return i;
}
@@ -864,10 +920,8 @@ static void nsim_setup(struct net_device *dev)
ether_setup(dev);
eth_hw_addr_random(dev);
dev->tx_queue_len = 0;
dev->flags &= ~IFF_MULTICAST;
dev->priv_flags |= IFF_LIVE_ADDR_CHANGE |
IFF_NO_QUEUE;
dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
dev->features |= NETIF_F_HIGHDMA |
NETIF_F_SG |
NETIF_F_FRAGLIST |