netdev - [PATCH 2/3] caif: Add support for flow-control on device's tx-queue

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Message-Id: <1322834777-2486-3-git-send-email-sjur.brandeland@stericsson.com>
Date:	Fri,  2 Dec 2011 15:06:16 +0100
From:	Sjur Brændeland <sjur.brandeland@...ricsson.com>
To:	netdev@...r.kernel.org
Cc:	David Miller <davem@...emloft.net>,
	Alexey Orishko <alexey.orishko@...ricsson.com>,
	Sjur Brændeland <sjur.brandeland@...ricsson.com>
Subject: [PATCH 2/3] 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 in order to detect when the last packet
put on queue is consumed. When this "hi-jacked" packet is consumed, flow-on
is sent upwards in the CAIF stack.

Signed-off-by: Sjur Brændeland <sjur.brandeland@...ricsson.com>
---
 net/caif/caif_dev.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 48 insertions(+), 0 deletions(-)

diff --git a/net/caif/caif_dev.c b/net/caif/caif_dev.c
index f7e8c70..415353e 100644
--- a/net/caif/caif_dev.c
+++ b/net/caif/caif_dev.c
@@ -34,6 +34,7 @@ struct caif_device_entry {
 	struct list_head list;
 	struct net_device *netdev;
 	int __percpu *pcpu_refcnt;
+	bool xoff;
 };
 
 struct caif_device_entry_list {
@@ -48,6 +49,7 @@ struct caif_net {
 };
 
 static int caif_net_id;
+static int q_high = 50; /* Percent */
 
 struct cfcnfg *get_cfcnfg(struct net *net)
 {
@@ -126,9 +128,28 @@ static struct caif_device_entry *caif_get(struct net_device *dev)
 	return NULL;
 }
 
+void caif_flow_cb(struct sk_buff *skb)
+{
+	struct caif_device_entry *caifd;
+	WARN_ON(skb->dev == NULL);
+
+	rcu_read_lock();
+	caifd = caif_get(skb->dev);
+	caifd->xoff = 0;
+	caifd_hold(caifd);
+	rcu_read_unlock();
+
+	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;
+	struct caif_dev_common *caifdev;
 	struct caif_device_entry *caifd =
 	    container_of(layer, struct caif_device_entry, layer);
 	struct sk_buff *skb;
@@ -137,6 +158,33 @@ static int transmit(struct cflayer *layer, struct cfpkt *pkt)
 	skb->dev = caifd->netdev;
 	skb_reset_network_header(skb);
 	skb->protocol = htons(ETH_P_CAIF);
+	caifdev = netdev_priv(caifd->netdev);
+
+	if (caifdev->flowctrl == NULL && caifd->netdev->tx_queue_len > 0 &&
+			!caifd->xoff) {
+		struct netdev_queue *txq;
+		int high;
+
+		txq = netdev_get_tx_queue(skb->dev, 0);
+		high = (caifd->netdev->tx_queue_len * q_high) / 100;
+
+		/* If we run with a TX queue, check if the queue is too long*/
+		if (netif_queue_stopped(caifd->netdev) ||
+			qdisc_qlen(txq->qdisc) > high) {
+
+			pr_debug("queue stop(%d) or full (%d>%d) - XOFF\n",
+					netif_queue_stopped(caifd->netdev),
+					qdisc_qlen(txq->qdisc), high);
+			caifd->xoff = 1;
+			/* Hijack this skb free callback function. */
+			skb_orphan(skb);
+			skb->destructor = caif_flow_cb;
+			caifd->layer.up->
+				ctrlcmd(caifd->layer.up,
+					_CAIF_CTRLCMD_PHYIF_FLOW_OFF_IND,
+					caifd->layer.id);
+		}
+	}
 
 	err = dev_queue_xmit(skb);
 	if (err > 0)
-- 
1.7.0.4

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