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 060135ceaf0e1a76615b2e6cd6830d42ac8becdf..a65779c6d72ff05a7f2273750464cc0f54b04d02 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);