rps: consistent rxhash

In case we compute a software skb->rxhash, we can generate a consistent
hash : Its value will be the same in both flow directions.

This helps some workloads, like conntracking, since the same state needs
to be accessed in both directions.

tbench + RFS + this patch gives better results than tbench with default
kernel configuration (no RPS, no RFS)

Also fixed some sparse warnings.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 7 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 7f5755b0a57c..0d78e0454a6d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1974,7 +1974,7 @@ u16 skb_tx_hash(const struct net_device *dev, const struct sk_buff *skb)
         if (skb->sk && skb->sk->sk_hash)
                 hash = skb->sk->sk_hash;
         else
-                hash = skb->protocol;
+                hash = (__force u16) skb->protocol;
 
         hash = jhash_1word(hash, hashrnd);
 
@@ -2253,8 +2253,8 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 
                 ip = (struct iphdr *) skb->data;
                 ip_proto = ip->protocol;
-                addr1 = ip->saddr;
-                addr2 = ip->daddr;
+                addr1 = (__force u32) ip->saddr;
+                addr2 = (__force u32) ip->daddr;
                 ihl = ip->ihl;
                 break;
         case __constant_htons(ETH_P_IPV6):
@@ -2263,8 +2263,8 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
 
                 ip6 = (struct ipv6hdr *) skb->data;
                 ip_proto = ip6->nexthdr;
-                addr1 = ip6->saddr.s6_addr32[3];
-                addr2 = ip6->daddr.s6_addr32[3];
+                addr1 = (__force u32) ip6->saddr.s6_addr32[3];
+                addr2 = (__force u32) ip6->daddr.s6_addr32[3];
                 ihl = (40 >> 2);
                 break;
         default:
@@ -2279,14 +2279,25 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
         case IPPROTO_AH:
         case IPPROTO_SCTP:
         case IPPROTO_UDPLITE:
-                if (pskb_may_pull(skb, (ihl * 4) + 4))
-                        ports = *((u32 *) (skb->data + (ihl * 4)));
+                if (pskb_may_pull(skb, (ihl * 4) + 4)) {
+                        __be16 *hports = (__be16 *) (skb->data + (ihl * 4));
+                        u32 sport, dport;
+
+                        sport = (__force u16) hports[0];
+                        dport = (__force u16) hports[1];
+                        if (dport < sport)
+                                swap(sport, dport);
+                        ports = (sport << 16) + dport;
+                }
                 break;
 
         default:
                 break;
         }
 
+        /* get a consistent hash (same value on both flow directions) */
+        if (addr2 < addr1)
+                swap(addr1, addr2);
         skb->rxhash = jhash_3words(addr1, addr2, ports, hashrnd);
         if (!skb->rxhash)
                 skb->rxhash = 1;