net: eliminate refcounting in backlog queue

Avoid the overhead of atomic increment/decrement on each received packet.
This helps performance of non-NAPI devices (like loopback).
Use cleanup function to walk queue on each cpu and clean out any
left over packets.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 7 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index cbf80098980c..fc6c9881eca8 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1909,7 +1909,6 @@ int netif_rx(struct sk_buff *skb)
         if (queue->input_pkt_queue.qlen <= netdev_max_backlog) {
                 if (queue->input_pkt_queue.qlen) {
 enqueue:
-                        dev_hold(skb->dev);
                         __skb_queue_tail(&queue->input_pkt_queue, skb);
                         local_irq_restore(flags);
                         return NET_RX_SUCCESS;
@@ -2270,6 +2269,20 @@ out:
         return ret;
 }
 
+/* Network device is going away, flush any packets still pending  */
+static void flush_backlog(void *arg)
+{
+        struct net_device *dev = arg;
+        struct softnet_data *queue = &__get_cpu_var(softnet_data);
+        struct sk_buff *skb, *tmp;
+
+        skb_queue_walk_safe(&queue->input_pkt_queue, skb, tmp)
+                if (skb->dev == dev) {
+                        __skb_unlink(skb, &queue->input_pkt_queue);
+                        kfree_skb(skb);
+                }
+}
+
 static int process_backlog(struct napi_struct *napi, int quota)
 {
         int work = 0;
@@ -2279,7 +2292,6 @@ static int process_backlog(struct napi_struct *napi, int quota)
         napi->weight = weight_p;
         do {
                 struct sk_buff *skb;
-                struct net_device *dev;
 
                 local_irq_disable();
                 skb = __skb_dequeue(&queue->input_pkt_queue);
@@ -2288,14 +2300,9 @@ static int process_backlog(struct napi_struct *napi, int quota)
                         local_irq_enable();
                         break;
                 }
-
                 local_irq_enable();
 
-                dev = skb->dev;
-
                 netif_receive_skb(skb);
-
-                dev_put(dev);
         } while (++work < quota && jiffies == start_time);
 
         return work;
@@ -4169,6 +4176,8 @@ void netdev_run_todo(void)
 
                 dev->reg_state = NETREG_UNREGISTERED;
 
+                on_each_cpu(flush_backlog, dev, 1);
+
                 netdev_wait_allrefs(dev);
 
                 /* paranoia */