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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
Download Patch File Download Diff File Expand all files Collapse all files

10
net/ipv4/tcp_output.c
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@ -995,7 +995,7 @@ static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
/* Advance write_seq and place onto the write_queue. */
tp->write_seq = TCP_SKB_CB(skb)->end_seq;
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);
@ -1167,7 +1167,7 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
}
/* Link BUFF into the send queue. */
skb_header_release(buff);
__skb_header_release(buff);
tcp_insert_write_queue_after(skb, buff, sk);
return 0;
@ -1671,7 +1671,7 @@ static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
tcp_set_skb_tso_segs(sk, buff, mss_now);
/* Link BUFF into the send queue. */
skb_header_release(buff);
__skb_header_release(buff);
tcp_insert_write_queue_after(skb, buff, sk);
return 0;
@ -2772,7 +2772,7 @@ int tcp_send_synack(struct sock *sk)
if (nskb == NULL)
return -ENOMEM;
tcp_unlink_write_queue(skb, sk);
skb_header_release(nskb);
__skb_header_release(nskb);
__tcp_add_write_queue_head(sk, nskb);
sk_wmem_free_skb(sk, skb);
sk->sk_wmem_queued += nskb->truesize;
@ -2947,7 +2947,7 @@ static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
tcb->end_seq += skb->len;
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);