core: Factor out flow calculation from get_rps_cpu

Factor out flow calculation code from get_rps_cpu, since other
functions can use the same code.

Revisions:

v2 (Ben): Separate flow calcuation out and use in select queue.
v3 (Arnd): Don't re-implement MIN.
v4 (Changli): skb->data points to ethernet header in macvtap, and
	make a fast path. Tested macvtap with this patch.
v5 (Changli):
	- Cache skb->rxhash in skb_get_rxhash
	- macvtap may not have pow(2) queues, so change code for
	  queue selection.
    (Arnd):
	- Use first available queue if all fails.

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -558,6 +558,15 @@ extern unsigned int   skb_find_text(struct sk_buff *skb, unsigned int from,
 				    unsigned int to, struct ts_config *config,
 				    struct ts_state *state);
 
+extern __u32 __skb_get_rxhash(struct sk_buff *skb);
+static inline __u32 skb_get_rxhash(struct sk_buff *skb)
+{
+	if (!skb->rxhash)
+		skb->rxhash = __skb_get_rxhash(skb);
+
+	return skb->rxhash;
+}
+
 #ifdef NET_SKBUFF_DATA_USES_OFFSET
 static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
 {

net/core/dev.c

@@ -2259,6 +2259,83 @@ static inline void ____napi_schedule(struct softnet_data *sd,
 	__raise_softirq_irqoff(NET_RX_SOFTIRQ);
 }
 
+/*
+ * __skb_get_rxhash: calculate a flow hash based on src/dst addresses
+ * and src/dst port numbers. Returns a non-zero hash number on success
+ * and 0 on failure.
+ */
+__u32 __skb_get_rxhash(struct sk_buff *skb)
+{
+	int nhoff, hash = 0;
+	struct ipv6hdr *ip6;
+	struct iphdr *ip;
+	u8 ip_proto;
+	u32 addr1, addr2, ihl;
+	union {
+		u32 v32;
+		u16 v16[2];
+	} ports;
+
+	nhoff = skb_network_offset(skb);
+
+	switch (skb->protocol) {
+	case __constant_htons(ETH_P_IP):
+		if (!pskb_may_pull(skb, sizeof(*ip) + nhoff))
+			goto done;
+
+		ip = (struct iphdr *) skb->data + nhoff;
+		ip_proto = ip->protocol;
+		addr1 = (__force u32) ip->saddr;
+		addr2 = (__force u32) ip->daddr;
+		ihl = ip->ihl;
+		break;
+	case __constant_htons(ETH_P_IPV6):
+		if (!pskb_may_pull(skb, sizeof(*ip6) + nhoff))
+			goto done;
+
+		ip6 = (struct ipv6hdr *) skb->data + nhoff;
+		ip_proto = ip6->nexthdr;
+		addr1 = (__force u32) ip6->saddr.s6_addr32[3];
+		addr2 = (__force u32) ip6->daddr.s6_addr32[3];
+		ihl = (40 >> 2);
+		break;
+	default:
+		goto done;
+	}
+
+	switch (ip_proto) {
+	case IPPROTO_TCP:
+	case IPPROTO_UDP:
+	case IPPROTO_DCCP:
+	case IPPROTO_ESP:
+	case IPPROTO_AH:
+	case IPPROTO_SCTP:
+	case IPPROTO_UDPLITE:
+		if (pskb_may_pull(skb, (ihl * 4) + 4 + nhoff)) {
+			ports.v32 = * (__force u32 *) (skb->data + nhoff +
+						       (ihl * 4));
+			if (ports.v16[1] < ports.v16[0])
+				swap(ports.v16[0], ports.v16[1]);
+			break;
+		}
+	default:
+		ports.v32 = 0;
+		break;
+	}
+
+	/* get a consistent hash (same value on both flow directions) */
+	if (addr2 < addr1)
+		swap(addr1, addr2);
+
+	hash = jhash_3words(addr1, addr2, ports.v32, hashrnd);
+	if (!hash)
+		hash = 1;
+
+done:
+	return hash;
+}
+EXPORT_SYMBOL(__skb_get_rxhash);
+
 #ifdef CONFIG_RPS
 
 /* One global table that all flow-based protocols share. */
@@ -2273,20 +2350,12 @@ EXPORT_SYMBOL(rps_sock_flow_table);
 static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 		       struct rps_dev_flow **rflowp)
 {
-	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);
@@ -2303,60 +2372,9 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 	if (!rxqueue->rps_map && !rxqueue->rps_flow_table)
 		goto done;
 
-	if (skb->rxhash)
-		goto got_hash; /* Skip hash computation on packet header */
-
-	switch (skb->protocol) {
-	case __constant_htons(ETH_P_IP):
-		if (!pskb_may_pull(skb, sizeof(*ip)))
-			goto done;
-
-		ip = (struct iphdr *) skb->data;
-		ip_proto = ip->protocol;
-		addr1 = (__force u32) ip->saddr;
-		addr2 = (__force u32) ip->daddr;
-		ihl = ip->ihl;
-		break;
-	case __constant_htons(ETH_P_IPV6):
-		if (!pskb_may_pull(skb, sizeof(*ip6)))
-			goto done;
-
-		ip6 = (struct ipv6hdr *) skb->data;
-		ip_proto = ip6->nexthdr;
-		addr1 = (__force u32) ip6->saddr.s6_addr32[3];
-		addr2 = (__force u32) ip6->daddr.s6_addr32[3];
-		ihl = (40 >> 2);
-		break;
-	default:
+	if (!skb_get_rxhash(skb))
 		goto done;
-	}
-	switch (ip_proto) {
-	case IPPROTO_TCP:
-	case IPPROTO_UDP:
-	case IPPROTO_DCCP:
-	case IPPROTO_ESP:
-	case IPPROTO_AH:
-	case IPPROTO_SCTP:
-	case IPPROTO_UDPLITE:
-		if (pskb_may_pull(skb, (ihl * 4) + 4)) {
-			ports.v32 = * (__force u32 *) (skb->data + (ihl * 4));
-			if (ports.v16[1] < ports.v16[0])
-				swap(ports.v16[0], ports.v16[1]);
-			break;
-		}
-	default:
-		ports.v32 = 0;
-		break;
-	}
 
-	/* 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;
-
-got_hash:
 	flow_table = rcu_dereference(rxqueue->rps_flow_table);
 	sock_flow_table = rcu_dereference(rps_sock_flow_table);
 	if (flow_table && sock_flow_table) {