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Message-ID: <1411428572.26859.165.camel@edumazet-glaptop2.roam.corp.google.com>
Date: Mon, 22 Sep 2014 16:29:32 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>
Subject: [PATCH net-next] net: introduce __skb_header_release()
From: Eric Dumazet <edumazet@...gle.com>
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@...gle.com>
---
include/linux/skbuff.h | 15 +++++++++++++++
net/core/skbuff.c | 4 ++--
net/ipv4/tcp.c | 4 ++--
net/ipv4/tcp_output.c | 10 +++++-----
4 files changed, 24 insertions(+), 9 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f1bfa3781c75..8eaa62400fca 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -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)
{
@@ -1092,6 +1093,20 @@ static inline void skb_header_release(struct sk_buff *skb)
}
/**
+ * __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
*
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 06a8feb10099..512dc7dcbc32 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -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:
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 070aeff1b131..553b01f52f71 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -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);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8c61a7c0c889..f173b1c4f815 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -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);
--
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