tun: compute the RFS hash only if needed.

The tun XDP sendmsg code path, unconditionally computes the symmetric
hash of each packet for RFS's sake, even when we could skip it. e.g.
when the device has a single queue.

This change adds the check already in-place for the skb sendmsg path
to avoid unneeded hashing.

The above gives small, but measurable, performance gain for VM xmit
path when zerocopy is not enabled.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 060135c..a65779c 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2448,7 +2448,8 @@ build:
                        goto out;
        }
 
-       if (!rcu_dereference(tun->steering_prog))
+       if (!rcu_dereference(tun->steering_prog) && tun->numqueues > 1 &&
+           !tfile->detached)
                rxhash = __skb_get_hash_symmetric(skb);
 
        netif_receive_skb(skb);