net: use jump_label to shortcut RPS if not setup

Most machines dont use RPS/RFS, and pay a fair amount of instructions in
netif_receive_skb() / netif_rx() / get_rps_cpu() just to discover
RPS/RFS is not setup.

Add a jump_label named rps_needed.

If no device rps_map or global rps_sock_flow_table is setup,
netif_receive_skb() / netif_rx() do a single instruction instead of many
ones, including conditional jumps.

jmp +0    (if CONFIG_JUMP_LABEL=y)

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

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 4d5698a..0bbe030 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -214,6 +214,11 @@ enum {
 #include <linux/cache.h>
 #include <linux/skbuff.h>
 
+#ifdef CONFIG_RPS
+#include <linux/jump_label.h>
+extern struct jump_label_key rps_needed;
+#endif
+
 struct neighbour;
 struct neigh_parms;
 struct sk_buff;

diff --git a/net/core/dev.c b/net/core/dev.c
index 26c49d5..f789599 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2711,6 +2711,8 @@ EXPORT_SYMBOL(__skb_get_rxhash);
 struct rps_sock_flow_table __rcu *rps_sock_flow_table __read_mostly;
 EXPORT_SYMBOL(rps_sock_flow_table);
 
+struct jump_label_key rps_needed __read_mostly;
+
 static struct rps_dev_flow *
 set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
            struct rps_dev_flow *rflow, u16 next_cpu)
@@ -2994,7 +2996,7 @@ int netif_rx(struct sk_buff *skb)
 
        trace_netif_rx(skb);
 #ifdef CONFIG_RPS
-       {
+       if (static_branch(&rps_needed)) {
                struct rps_dev_flow voidflow, *rflow = &voidflow;
                int cpu;
 
@@ -3009,14 +3011,13 @@ int netif_rx(struct sk_buff *skb)
 
                rcu_read_unlock();
                preempt_enable();
-       }
-#else
+       } else
+#endif
        {
                unsigned int qtail;
                ret = enqueue_to_backlog(skb, get_cpu(), &qtail);
                put_cpu();
        }
-#endif
        return ret;
 }
 EXPORT_SYMBOL(netif_rx);
@@ -3359,7 +3360,7 @@ int netif_receive_skb(struct sk_buff *skb)
                return NET_RX_SUCCESS;
 
 #ifdef CONFIG_RPS
-       {
+       if (static_branch(&rps_needed)) {
                struct rps_dev_flow voidflow, *rflow = &voidflow;
                int cpu, ret;
 
@@ -3370,16 +3371,12 @@ int netif_receive_skb(struct sk_buff *skb)
                if (cpu >= 0) {
                        ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail);
                        rcu_read_unlock();
-               } else {
-                       rcu_read_unlock();
-                       ret = __netif_receive_skb(skb);
+                       return ret;
                }
-
-               return ret;
+               rcu_read_unlock();
        }
-#else
-       return __netif_receive_skb(skb);
 #endif
+       return __netif_receive_skb(skb);
 }
 EXPORT_SYMBOL(netif_receive_skb);
 

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 602b141..db6c2f8 100644 (file)
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -606,9 +606,12 @@ static ssize_t store_rps_map(struct netdev_rx_queue *queue,
        rcu_assign_pointer(queue->rps_map, map);
        spin_unlock(&rps_map_lock);
 
-       if (old_map)
+       if (map)
+               jump_label_inc(&rps_needed);
+       if (old_map) {
                kfree_rcu(old_map, rcu);
-
+               jump_label_dec(&rps_needed);
+       }
        free_cpumask_var(mask);
        return len;
 }

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 77a65f0..d05559d 100644 (file)
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -68,8 +68,13 @@ static int rps_sock_flow_sysctl(ctl_table *table, int write,
 
                if (sock_table != orig_sock_table) {
                        rcu_assign_pointer(rps_sock_flow_table, sock_table);
-                       synchronize_rcu();
-                       vfree(orig_sock_table);
+                       if (sock_table)
+                               jump_label_inc(&rps_needed);
+                       if (orig_sock_table) {
+                               jump_label_dec(&rps_needed);
+                               synchronize_rcu();
+                               vfree(orig_sock_table);
+                       }
                }
        }