net: ip_rt_send_redirect() optimization

While doing some forwarding benchmarks, I noticed
ip_rt_send_redirect() is rather expensive, even if send_redirects is
false for the device.

Fix is to avoid two atomic ops, we dont really need to take a
reference on in_dev

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

1 files changed, 11 insertions, 9 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index fafbe163e2b5..91867d3e6328 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1514,13 +1514,17 @@ static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst)
 void ip_rt_send_redirect(struct sk_buff *skb)
 {
         struct rtable *rt = skb_rtable(skb);
-        struct in_device *in_dev = in_dev_get(rt->u.dst.dev);
+        struct in_device *in_dev;
+        int log_martians;
 
-        if (!in_dev)
+        rcu_read_lock();
+        in_dev = __in_dev_get_rcu(rt->u.dst.dev);
+        if (!in_dev || !IN_DEV_TX_REDIRECTS(in_dev)) {
+                rcu_read_unlock();
                 return;
-
-        if (!IN_DEV_TX_REDIRECTS(in_dev))
-                goto out;
+        }
+        log_martians = IN_DEV_LOG_MARTIANS(in_dev);
+        rcu_read_unlock();
 
         /* No redirected packets during ip_rt_redirect_silence;
          * reset the algorithm.
@@ -1533,7 +1537,7 @@ void ip_rt_send_redirect(struct sk_buff *skb)
          */
         if (rt->u.dst.rate_tokens >= ip_rt_redirect_number) {
                 rt->u.dst.rate_last = jiffies;
-                goto out;
+                return;
         }
 
         /* Check for load limit; set rate_last to the latest sent
@@ -1547,7 +1551,7 @@ void ip_rt_send_redirect(struct sk_buff *skb)
                 rt->u.dst.rate_last = jiffies;
                 ++rt->u.dst.rate_tokens;
 #ifdef CONFIG_IP_ROUTE_VERBOSE
-                if (IN_DEV_LOG_MARTIANS(in_dev) &&
+                if (log_martians &&
                     rt->u.dst.rate_tokens == ip_rt_redirect_number &&
                     net_ratelimit())
                         printk(KERN_WARNING "host %pI4/if%d ignores redirects for %pI4 to %pI4.\n",
@@ -1555,8 +1559,6 @@ void ip_rt_send_redirect(struct sk_buff *skb)
                                 &rt->rt_dst, &rt->rt_gateway);
 #endif
         }
-out:
-        in_dev_put(in_dev);
 }
 
 static int ip_error(struct sk_buff *skb)