caif: Add support for flow-control on device's tx-queue
Flow control is implemented by inspecting the qdisc queue length
in order to detect potential overflow on the TX queue. When a threshold
is reached flow-off is sent upwards in the CAIF stack. At the same time
the skb->destructor is hi-jacked by orphaning the SKB and the original
destructor is replaced with a "flow-on" callback. When the "hi-jacked"
SKB is consumed the queue should be empty, and the "flow-on" callback
is called and xon is sent upwards in the CAIF stack.
Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/caif/caif_dev.c b/net/caif/caif_dev.c
index 6acec19..74c1273 100644
--- a/net/caif/caif_dev.c
+++ b/net/caif/caif_dev.c
@@ -17,6 +17,7 @@
#include <linux/netdevice.h>
#include <linux/mutex.h>
#include <linux/module.h>
+#include <linux/spinlock.h>
#include <net/netns/generic.h>
#include <net/net_namespace.h>
#include <net/pkt_sched.h>
@@ -34,6 +35,8 @@
struct list_head list;
struct net_device *netdev;
int __percpu *pcpu_refcnt;
+ spinlock_t flow_lock;
+ bool xoff;
};
struct caif_device_entry_list {
@@ -48,6 +51,7 @@
};
static int caif_net_id;
+static int q_high = 50; /* Percent */
struct cfcnfg *get_cfcnfg(struct net *net)
{
@@ -126,17 +130,94 @@
return NULL;
}
+void caif_flow_cb(struct sk_buff *skb)
+{
+ struct caif_device_entry *caifd;
+ bool send_xoff;
+
+ WARN_ON(skb->dev == NULL);
+
+ rcu_read_lock();
+ caifd = caif_get(skb->dev);
+ caifd_hold(caifd);
+ rcu_read_unlock();
+
+ spin_lock_bh(&caifd->flow_lock);
+ send_xoff = caifd->xoff;
+ caifd->xoff = 0;
+ spin_unlock_bh(&caifd->flow_lock);
+
+ if (send_xoff)
+ caifd->layer.up->
+ ctrlcmd(caifd->layer.up,
+ _CAIF_CTRLCMD_PHYIF_FLOW_ON_IND,
+ caifd->layer.id);
+ caifd_put(caifd);
+}
+
static int transmit(struct cflayer *layer, struct cfpkt *pkt)
{
- int err;
+ int err, high = 0, qlen = 0;
+ struct caif_dev_common *caifdev;
struct caif_device_entry *caifd =
container_of(layer, struct caif_device_entry, layer);
struct sk_buff *skb;
+ struct netdev_queue *txq;
+
+ rcu_read_lock_bh();
skb = cfpkt_tonative(pkt);
skb->dev = caifd->netdev;
skb_reset_network_header(skb);
skb->protocol = htons(ETH_P_CAIF);
+ caifdev = netdev_priv(caifd->netdev);
+
+ /* Check if we need to handle xoff */
+ if (likely(caifd->netdev->tx_queue_len == 0))
+ goto noxoff;
+
+ if (unlikely(caifd->xoff))
+ goto noxoff;
+
+ if (likely(!netif_queue_stopped(caifd->netdev))) {
+ /* If we run with a TX queue, check if the queue is too long*/
+ txq = netdev_get_tx_queue(skb->dev, 0);
+ qlen = qdisc_qlen(rcu_dereference_bh(txq->qdisc));
+
+ if (likely(qlen == 0))
+ goto noxoff;
+
+ high = (caifd->netdev->tx_queue_len * q_high) / 100;
+ if (likely(qlen < high))
+ goto noxoff;
+ }
+
+ /* Hold lock while accessing xoff */
+ spin_lock_bh(&caifd->flow_lock);
+ if (caifd->xoff) {
+ spin_unlock_bh(&caifd->flow_lock);
+ goto noxoff;
+ }
+
+ /*
+ * Handle flow off, we do this by temporary hi-jacking this
+ * skb's destructor function, and replace it with our own
+ * flow-on callback. The callback will set flow-on and call
+ * the original destructor.
+ */
+
+ pr_debug("queue has stopped(%d) or is full (%d > %d)\n",
+ netif_queue_stopped(caifd->netdev),
+ qlen, high);
+ caifd->xoff = 1;
+ spin_unlock_bh(&caifd->flow_lock);
+ skb_orphan(skb);
+
+ caifd->layer.up->ctrlcmd(caifd->layer.up,
+ _CAIF_CTRLCMD_PHYIF_FLOW_OFF_IND,
+ caifd->layer.id);
+noxoff:
+ rcu_read_unlock_bh();
err = dev_queue_xmit(skb);
if (err > 0)
@@ -232,6 +313,7 @@
if (!caifd)
return;
*layer = &caifd->layer;
+ spin_lock_init(&caifd->flow_lock);
switch (caifdev->link_select) {
case CAIF_LINK_HIGH_BANDW:
@@ -316,6 +398,7 @@
break;
}
+ caifd->xoff = 0;
cfcnfg_set_phy_state(cfg, &caifd->layer, true);
rcu_read_unlock();