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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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15
include/linux/skbuff.h
View file

@ -1083,6 +1083,7 @@ static inline int skb_header_cloned(const struct sk_buff *skb)
* Drop a reference to the header part of the buffer. This is done
* by acquiring a payload reference. You must not read from the header
* part of skb->data after this.
* Note : Check if you can use __skb_header_release() instead.
*/
static inline void skb_header_release(struct sk_buff *skb)
{
@ -1091,6 +1092,20 @@ static inline void skb_header_release(struct sk_buff *skb)
atomic_add(1 << SKB_DATAREF_SHIFT, &skb_shinfo(skb)->dataref);
}
/**
* __skb_header_release - release reference to header
* @skb: buffer to operate on
*
* Variant of skb_header_release() assuming skb is private to caller.
* We can avoid one atomic operation.
*/
static inline void __skb_header_release(struct sk_buff *skb)
{
skb->nohdr = 1;
atomic_set(&skb_shinfo(skb)->dataref, 1 + (1 << SKB_DATAREF_SHIFT));
}
/**
* skb_shared - is the buffer shared
* @skb: buffer to check

4
net/core/skbuff.c
View file

@ -3179,7 +3179,7 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
skb_shinfo(nskb)->frag_list = p;
skb_shinfo(nskb)->gso_size = pinfo->gso_size;
pinfo->gso_size = 0;
skb_header_release(p);
__skb_header_release(p);
NAPI_GRO_CB(nskb)->last = p;
nskb->data_len += p->len;
@ -3211,7 +3211,7 @@ merge:
else
NAPI_GRO_CB(p)->last->next = skb;
NAPI_GRO_CB(p)->last = skb;
skb_header_release(skb);
__skb_header_release(skb);
lp = p;
done:

4
net/ipv4/tcp.c
View file

@ -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);

10
net/ipv4/tcp_output.c
View file

@ -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);