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net: introduce __skb_header_release()

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While profiling TCP stack, I noticed one useless atomic operation
in tcp_sendmsg(), caused by skb_header_release().

It turns out all current skb_header_release() users have a fresh skb,
that no other user can see, so we can avoid one atomic operation.

Introduce __skb_header_release() to clearly document this.

This gave me a 1.5 % improvement on TCP_RR workload.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2014-09-22 16:29:32 -07:00 • committed by David S. Miller
parent aebac74493
commit f4a775d144
4 changed files with 24 additions and 9 deletions
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4
net/ipv4/tcp.c
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@ -609,7 +609,7 @@ static inline bool forced_push(const struct tcp_sock *tp)
return after(tp->write_seq, tp->pushed_seq + (tp->max_window >> 1));
}
static inline void skb_entail(struct sock *sk, struct sk_buff *skb)
static void skb_entail(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
@ -618,7 +618,7 @@ static inline void skb_entail(struct sock *sk, struct sk_buff *skb)
tcb->seq = tcb->end_seq = tp->write_seq;
tcb->tcp_flags = TCPHDR_ACK;
tcb->sacked = 0;
skb_header_release(skb);
__skb_header_release(skb);
tcp_add_write_queue_tail(sk, skb);
sk->sk_wmem_queued += skb->truesize;
sk_mem_charge(sk, skb->truesize);