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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
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@@ -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