net: introduce dev_consume_skb_any()

Some network drivers use dev_kfree_skb_any() and dev_kfree_skb_irq()
helpers to free skbs, both for dropped packets and TX completed ones.

We need to separate the two causes to get better diagnostics
given by dropwatch or "perf record -e skb:kfree_skb"

This patch provides two new helpers, dev_consume_skb_any() and
dev_consume_skb_irq() to be used for consumed skbs.

__dev_kfree_skb_irq() is slightly optimized to remove one
atomic_dec_and_test() in fast path, and use this_cpu_{r|w} accessors.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 30 insertions, 15 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index c98052487e98..6cc98dd49c7a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2145,30 +2145,42 @@ void __netif_schedule(struct Qdisc *q)
 }
 EXPORT_SYMBOL(__netif_schedule);
 
-void dev_kfree_skb_irq(struct sk_buff *skb)
+struct dev_kfree_skb_cb {
+        enum skb_free_reason reason;
+};
+
+static struct dev_kfree_skb_cb *get_kfree_skb_cb(const struct sk_buff *skb)
+{
+        return (struct dev_kfree_skb_cb *)skb->cb;
+}
+
+void __dev_kfree_skb_irq(struct sk_buff *skb, enum skb_free_reason reason)
 {
-        if (atomic_dec_and_test(&skb->users)) {
-                struct softnet_data *sd;
-                unsigned long flags;
+        unsigned long flags;
 
-                local_irq_save(flags);
-                sd = &__get_cpu_var(softnet_data);
-                skb->next = sd->completion_queue;
-                sd->completion_queue = skb;
-                raise_softirq_irqoff(NET_TX_SOFTIRQ);
-                local_irq_restore(flags);
+        if (likely(atomic_read(&skb->users) == 1)) {
+                smp_rmb();
+                atomic_set(&skb->users, 0);
+        } else if (likely(!atomic_dec_and_test(&skb->users))) {
+                return;
         }
+        get_kfree_skb_cb(skb)->reason = reason;
+        local_irq_save(flags);
+        skb->next = __this_cpu_read(softnet_data.completion_queue);
+        __this_cpu_write(softnet_data.completion_queue, skb);
+        raise_softirq_irqoff(NET_TX_SOFTIRQ);
+        local_irq_restore(flags);
 }
-EXPORT_SYMBOL(dev_kfree_skb_irq);
+EXPORT_SYMBOL(__dev_kfree_skb_irq);
 
-void dev_kfree_skb_any(struct sk_buff *skb)
+void __dev_kfree_skb_any(struct sk_buff *skb, enum skb_free_reason reason)
 {
         if (in_irq() || irqs_disabled())
-                dev_kfree_skb_irq(skb);
+                __dev_kfree_skb_irq(skb, reason);
         else
                 dev_kfree_skb(skb);
 }
-EXPORT_SYMBOL(dev_kfree_skb_any);
+EXPORT_SYMBOL(__dev_kfree_skb_any);
 
 
 /**
@@ -3306,7 +3318,10 @@ static void net_tx_action(struct softirq_action *h)
                         clist = clist->next;
 
                         WARN_ON(atomic_read(&skb->users));
-                        trace_kfree_skb(skb, net_tx_action);
+                        if (likely(get_kfree_skb_cb(skb)->reason == SKB_REASON_CONSUMED))
+                                trace_consume_skb(skb);
+                        else
+                                trace_kfree_skb(skb, net_tx_action);
                         __kfree_skb(skb);
                 }
         }