rps: Inspect GRE encapsulated packets to get flow hash

Crack open GRE packets in __skb_get_rxhash to compute 4-tuple hash on
in encapsulated packet.  Note that this is used only when the
__skb_get_rxhash is taken, in particular only when the device does
not compute provide the rxhash (ie. feature is disabled).

This was tested by creating a single GRE tunnel between two 16 core
AMD machines.  200 netperf TCP_RR streams were ran with 1 byte
request and response size.

Without patch: 157497 tps, 50/90/99% latencies 1250/1292/1364 usecs
With patch: 325896 tps, 50/90/99% latencies 603/848/1169

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 4bee9a9aeef6..a8d91a5dd909 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2570,6 +2570,28 @@ again:
         }
 
         switch (ip_proto) {
+        case IPPROTO_GRE:
+                if (pskb_may_pull(skb, nhoff + 16)) {
+                        u8 *h = skb->data + nhoff;
+                        __be16 flags = *(__be16 *)h;
+
+                        /*
+                         * Only look inside GRE if version zero and no
+                         * routing
+                         */
+                        if (!(flags & (GRE_VERSION|GRE_ROUTING))) {
+                                proto = *(__be16 *)(h + 2);
+                                nhoff += 4;
+                                if (flags & GRE_CSUM)
+                                        nhoff += 4;
+                                if (flags & GRE_KEY)
+                                        nhoff += 4;
+                                if (flags & GRE_SEQ)
+                                        nhoff += 4;
+                                goto again;
+                        }
+                }
+                break;
         default:
                 break;
         }