[PATCH v2 1/2] core: Factor out flow calculation from get_rps_cpu

[Krishna Kumar <krkumar2@in.ibm.com>]

From: Krishna Kumar <krkumar2@in.ibm.com>

Factor out flow calculation code from get_rps_cpu, since macvtap
driver can use the same code.

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
---
 net/core/dev.c |   94 +++++++++++++++++++++++++++++------------------
 1 file changed, 58 insertions(+), 36 deletions(-)

diff -ruNp org/net/core/dev.c new/net/core/dev.c
--- org/net/core/dev.c	2010-08-02 10:06:59.000000000 +0530
+++ new/net/core/dev.c	2010-08-02 19:29:34.000000000 +0530
@@ -2263,51 +2263,24 @@ static inline void ____napi_schedule(str
 	__raise_softirq_irqoff(NET_RX_SOFTIRQ);
 }
 
-#ifdef CONFIG_RPS
-
-/* One global table that all flow-based protocols share. */
-struct rps_sock_flow_table *rps_sock_flow_table __read_mostly;
-EXPORT_SYMBOL(rps_sock_flow_table);
-
 /*
- * get_rps_cpu is called from netif_receive_skb and returns the target
- * CPU from the RPS map of the receiving queue for a given skb.
- * rcu_read_lock must be held on entry.
+ * skb_calculate_flow: calculate a flow hash based on src/dst addresses
+ * and src/dst port numbers. On success, returns a hash number (> 0),
+ * otherwise -1.
  */
-static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
-		       struct rps_dev_flow **rflowp)
+int skb_calculate_flow(struct net_device *dev, struct sk_buff *skb)
 {
+	int hash = skb->rxhash;
 	struct ipv6hdr *ip6;
 	struct iphdr *ip;
-	struct netdev_rx_queue *rxqueue;
-	struct rps_map *map;
-	struct rps_dev_flow_table *flow_table;
-	struct rps_sock_flow_table *sock_flow_table;
-	int cpu = -1;
 	u8 ip_proto;
-	u16 tcpu;
 	u32 addr1, addr2, ihl;
 	union {
 		u32 v32;
 		u16 v16[2];
 	} ports;
 
-	if (skb_rx_queue_recorded(skb)) {
-		u16 index = skb_get_rx_queue(skb);
-		if (unlikely(index >= dev->num_rx_queues)) {
-			WARN_ONCE(dev->num_rx_queues > 1, "%s received packet "
-				"on queue %u, but number of RX queues is %u\n",
-				dev->name, index, dev->num_rx_queues);
-			goto done;
-		}
-		rxqueue = dev->_rx + index;
-	} else
-		rxqueue = dev->_rx;
-
-	if (!rxqueue->rps_map && !rxqueue->rps_flow_table)
-		goto done;
-
-	if (skb->rxhash)
+	if (hash)
 		goto got_hash; /* Skip hash computation on packet header */
 
 	switch (skb->protocol) {
@@ -2334,6 +2307,7 @@ static int get_rps_cpu(struct net_device
 	default:
 		goto done;
 	}
+
 	switch (ip_proto) {
 	case IPPROTO_TCP:
 	case IPPROTO_UDP:
@@ -2356,11 +2330,59 @@ static int get_rps_cpu(struct net_device
 	/* get a consistent hash (same value on both flow directions) */
 	if (addr2 < addr1)
 		swap(addr1, addr2);
-	skb->rxhash = jhash_3words(addr1, addr2, ports.v32, hashrnd);
-	if (!skb->rxhash)
-		skb->rxhash = 1;
+
+	hash = jhash_3words(addr1, addr2, ports.v32, hashrnd);
+	if (!hash)
+		hash = 1;
 
 got_hash:
+	return hash;
+
+done:
+	return -1;
+}
+EXPORT_SYMBOL(skb_calculate_flow);
+
+#ifdef CONFIG_RPS
+
+/* One global table that all flow-based protocols share. */
+struct rps_sock_flow_table *rps_sock_flow_table __read_mostly;
+EXPORT_SYMBOL(rps_sock_flow_table);
+
+/*
+ * get_rps_cpu is called from netif_receive_skb and returns the target
+ * CPU from the RPS map of the receiving queue for a given skb.
+ * rcu_read_lock must be held on entry.
+ */
+static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
+		       struct rps_dev_flow **rflowp)
+{
+	struct netdev_rx_queue *rxqueue;
+	struct rps_map *map;
+	struct rps_dev_flow_table *flow_table;
+	struct rps_sock_flow_table *sock_flow_table;
+	int cpu = -1;
+	u16 tcpu;
+
+	if (skb_rx_queue_recorded(skb)) {
+		u16 index = skb_get_rx_queue(skb);
+		if (unlikely(index >= dev->num_rx_queues)) {
+			WARN_ONCE(dev->num_rx_queues > 1, "%s received packet "
+				"on queue %u, but number of RX queues is %u\n",
+				dev->name, index, dev->num_rx_queues);
+			goto done;
+		}
+		rxqueue = dev->_rx + index;
+	} else
+		rxqueue = dev->_rx;
+
+	if (!rxqueue->rps_map && !rxqueue->rps_flow_table)
+		goto done;
+
+	skb->rxhash = skb_calculate_flow(dev, skb);
+	if (skb->rxhash < 0)
+		goto done;
+
 	flow_table = rcu_dereference(rxqueue->rps_flow_table);
 	sock_flow_table = rcu_dereference(rps_sock_flow_table);
 	if (flow_table && sock_flow_table) {