udp: avoid a cache miss on dequeue
Since UDP no more uses sk->destructor, we can clear completely
the skb head state before enqueuing. Amend and use
skb_release_head_state() for that.
All head states share a single cacheline, which is not
normally used/accesses on dequeue. We can avoid entirely accessing
such cacheline implementing and using in the UDP code a specialized
skb free helper which ignores the skb head state.
This saves a cacheline miss at skb deallocation time.
v1 -> v2:
replaced secpath_reset() with skb_release_head_state()
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 747263c..3046027 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -643,12 +643,10 @@ static void kfree_skbmem(struct sk_buff *skb)
kmem_cache_free(skbuff_fclone_cache, fclones);
}
-static void skb_release_head_state(struct sk_buff *skb)
+void skb_release_head_state(struct sk_buff *skb)
{
skb_dst_drop(skb);
-#ifdef CONFIG_XFRM
- secpath_put(skb->sp);
-#endif
+ secpath_reset(skb);
if (skb->destructor) {
WARN_ON(in_irq());
skb->destructor(skb);
@@ -751,6 +749,24 @@ void consume_skb(struct sk_buff *skb)
}
EXPORT_SYMBOL(consume_skb);
+/**
+ * consume_stateless_skb - free an skbuff, assuming it is stateless
+ * @skb: buffer to free
+ *
+ * Works like consume_skb(), but this variant assumes that all the head
+ * states have been already dropped.
+ */
+void consume_stateless_skb(struct sk_buff *skb)
+{
+ if (!skb_unref(skb))
+ return;
+
+ trace_consume_skb(skb);
+ if (likely(skb->head))
+ skb_release_data(skb);
+ kfree_skbmem(skb);
+}
+
void __kfree_skb_flush(void)
{
struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index fdcb743..d8b265f 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1359,7 +1359,8 @@ void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len)
sk_peek_offset_bwd(sk, len);
unlock_sock_fast(sk, slow);
}
- consume_skb(skb);
+
+ consume_stateless_skb(skb);
}
EXPORT_SYMBOL_GPL(skb_consume_udp);
@@ -1739,6 +1740,9 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
sk_mark_napi_id_once(sk, skb);
}
+ /* clear all pending head states while they are hot in the cache */
+ skb_release_head_state(skb);
+
rc = __udp_enqueue_schedule_skb(sk, skb);
if (rc < 0) {
int is_udplite = IS_UDPLITE(sk);