rps: keep the old behavior on SMP without rps

keep the old behavior on SMP without rps

RPS introduces a lock operation to per cpu variable input_pkt_queue on
SMP whenever rps is enabled or not. On SMP without RPS, this lock isn't
needed at all.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
----
net/core/dev.c | 42 ++++++++++++++++++++++++++++--------------
1 file changed, 28 insertions(+), 14 deletions(-)
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 28 insertions, 14 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 887aa84fcd46..427cd53c118d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -206,6 +206,20 @@ static inline struct hlist_head *dev_index_hash(struct net *net, int ifindex)
         return &net->dev_index_head[ifindex & (NETDEV_HASHENTRIES - 1)];
 }
 
+static inline void rps_lock(struct softnet_data *queue)
+{
+#ifdef CONFIG_RPS
+        spin_lock(&queue->input_pkt_queue.lock);
+#endif
+}
+
+static inline void rps_unlock(struct softnet_data *queue)
+{
+#ifdef CONFIG_RPS
+        spin_unlock(&queue->input_pkt_queue.lock);
+#endif
+}
+
 /* Device list insertion */
 static int list_netdevice(struct net_device *dev)
 {
@@ -2313,13 +2327,13 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu)
         local_irq_save(flags);
         __get_cpu_var(netdev_rx_stat).total++;
 
-        spin_lock(&queue->input_pkt_queue.lock);
+        rps_lock(queue);
         if (queue->input_pkt_queue.qlen <= netdev_max_backlog) {
                 if (queue->input_pkt_queue.qlen) {
 enqueue:
                         __skb_queue_tail(&queue->input_pkt_queue, skb);
-                        spin_unlock_irqrestore(&queue->input_pkt_queue.lock,
-                            flags);
+                        rps_unlock(queue);
+                        local_irq_restore(flags);
                         return NET_RX_SUCCESS;
                 }
 
@@ -2341,7 +2355,7 @@ enqueue:
                 goto enqueue;
         }
 
-        spin_unlock(&queue->input_pkt_queue.lock);
+        rps_unlock(queue);
 
         __get_cpu_var(netdev_rx_stat).dropped++;
         local_irq_restore(flags);
@@ -2766,19 +2780,19 @@ int netif_receive_skb(struct sk_buff *skb)
 EXPORT_SYMBOL(netif_receive_skb);
 
 /* Network device is going away, flush any packets still pending  */
-static void flush_backlog(struct net_device *dev, int cpu)
+static void flush_backlog(void *arg)
 {
-        struct softnet_data *queue = &per_cpu(softnet_data, cpu);
+        struct net_device *dev = arg;
+        struct softnet_data *queue = &__get_cpu_var(softnet_data);
         struct sk_buff *skb, *tmp;
-        unsigned long flags;
 
-        spin_lock_irqsave(&queue->input_pkt_queue.lock, flags);
+        rps_lock(queue);
         skb_queue_walk_safe(&queue->input_pkt_queue, skb, tmp)
                 if (skb->dev == dev) {
                         __skb_unlink(skb, &queue->input_pkt_queue);
                         kfree_skb(skb);
                 }
-        spin_unlock_irqrestore(&queue->input_pkt_queue.lock, flags);
+        rps_unlock(queue);
 }
 
 static int napi_gro_complete(struct sk_buff *skb)
@@ -3091,14 +3105,16 @@ static int process_backlog(struct napi_struct *napi, int quota)
         do {
                 struct sk_buff *skb;
 
-                spin_lock_irq(&queue->input_pkt_queue.lock);
+                local_irq_disable();
+                rps_lock(queue);
                 skb = __skb_dequeue(&queue->input_pkt_queue);
                 if (!skb) {
                         __napi_complete(napi);
                         spin_unlock_irq(&queue->input_pkt_queue.lock);
                         break;
                 }
-                spin_unlock_irq(&queue->input_pkt_queue.lock);
+                rps_unlock(queue);
+                local_irq_enable();
 
                 __netif_receive_skb(skb);
         } while (++work < quota && jiffies == start_time);
@@ -5548,7 +5564,6 @@ void netdev_run_todo(void)
         while (!list_empty(&list)) {
                 struct net_device *dev
                         = list_first_entry(&list, struct net_device, todo_list);
-                int i;
                 list_del(&dev->todo_list);
 
                 if (unlikely(dev->reg_state != NETREG_UNREGISTERING)) {
@@ -5560,8 +5575,7 @@ void netdev_run_todo(void)
 
                 dev->reg_state = NETREG_UNREGISTERED;
 
-                for_each_online_cpu(i)
-                        flush_backlog(dev, i);
+                on_each_cpu(flush_backlog, dev, 1);
 
                 netdev_wait_allrefs(dev);