net: introduce __skb_header_release()
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>
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8c61a7c..f173b1c 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -995,7 +995,7 @@
/* 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 @@
}
/* 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 @@
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 @@
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 @@
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);