[net-next 3/3] ip_gre: cache the device mtu hard_header_len calc

[William Tu]

The patch introduces ip_tunnel->ether_mtu fields to cache the value of
dev->mtu + dev->hard_header_len.  This avoids the arithmetic operation
on every packet.

Signed-off-by: William Tu <u9012...@gmail.com>
Cc: David Laight <david.lai...@aculab.com>
---
 include/net/ip_tunnels.h | 1 +
 net/ipv4/ip_gre.c        | 8 ++++----
 net/ipv4/ip_tunnel.c     | 3 +++
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
index b41a1e057fce..19565be26e13 100644
--- a/include/net/ip_tunnels.h
+++ b/include/net/ip_tunnels.h
@@ -117,6 +117,7 @@ struct ip_tunnel {
 
        /* This field used only by ERSPAN */
        u32             index;          /* ERSPAN type II index */
+       unsigned int    ether_mtu;      /* The mtu including the ether hdr */
 
        struct dst_cache dst_cache;
 
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 6e6e4c4811cc..994b8ddea0b1 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -578,8 +578,8 @@ static void erspan_fb_xmit(struct sk_buff *skb, struct 
net_device *dev,
        if (gre_handle_offloads(skb, false))
                goto err_free_rt;
 
-       if (skb->len > dev->mtu + dev->hard_header_len) {
-               pskb_trim(skb, dev->mtu + dev->hard_header_len);
+       if (skb->len > tunnel->ether_mtu) {
+               pskb_trim(skb, tunnel->ether_mtu);
                truncate = true;
        }
 
@@ -730,8 +730,8 @@ static netdev_tx_t erspan_xmit(struct sk_buff *skb,
        if (skb_cow_head(skb, dev->needed_headroom))
                goto free_skb;
 
-       if (skb->len > dev->mtu + dev->hard_header_len) {
-               pskb_trim(skb, dev->mtu + dev->hard_header_len);
+       if (skb->len > tunnel->ether_mtu) {
+               pskb_trim(skb, tunnel->ether_mtu);
                truncate = true;
        }
 
diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index fe6fee728ce4..859af5b86802 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -348,6 +348,7 @@ static int ip_tunnel_bind_dev(struct net_device *dev)
 
        dev->needed_headroom = t_hlen + hlen;
        mtu -= (dev->hard_header_len + t_hlen);
+       tunnel->ether_mtu = mtu + dev->hard_header_len;
 
        if (mtu < 68)
                mtu = 68;
@@ -952,6 +953,7 @@ int __ip_tunnel_change_mtu(struct net_device *dev, int 
new_mtu, bool strict)
        }
 
        dev->mtu = new_mtu;
+       tunnel->ether_mtu = new_mtu + dev->hard_header_len;
        return 0;
 }
 EXPORT_SYMBOL_GPL(__ip_tunnel_change_mtu);
@@ -1183,6 +1185,7 @@ int ip_tunnel_init(struct net_device *dev)
 
        tunnel->dev = dev;
        tunnel->net = dev_net(dev);
+       tunnel->ether_mtu = dev->mtu + dev->hard_header_len;
        strcpy(tunnel->parms.name, dev->name);
        iph->version            = 4;
        iph->ihl                = 5;
-- 
2.7.4